diff --git a/backend/src/main/java/org/raddatz/familienarchiv/controller/GlobalExceptionHandler.java b/backend/src/main/java/org/raddatz/familienarchiv/controller/GlobalExceptionHandler.java
index ece8292a..cd2b37d3 100644
--- a/backend/src/main/java/org/raddatz/familienarchiv/controller/GlobalExceptionHandler.java
+++ b/backend/src/main/java/org/raddatz/familienarchiv/controller/GlobalExceptionHandler.java
@@ -8,6 +8,7 @@ import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.MethodArgumentNotValidException;
 import org.springframework.web.bind.annotation.ExceptionHandler;
 import org.springframework.web.bind.annotation.RestControllerAdvice;
+import org.springframework.web.server.ResponseStatusException;
 
 import lombok.extern.slf4j.Slf4j;
 
@@ -30,6 +31,12 @@ public class GlobalExceptionHandler {
         return ResponseEntity.badRequest().body(new ErrorResponse(ErrorCode.VALIDATION_ERROR, message));
     }
 
+    @ExceptionHandler(ResponseStatusException.class)
+    public ResponseEntity<ErrorResponse> handleResponseStatus(ResponseStatusException ex) {
+        return ResponseEntity.status(ex.getStatusCode())
+                .body(new ErrorResponse(ErrorCode.VALIDATION_ERROR, ex.getReason()));
+    }
+
     @ExceptionHandler(Exception.class)
     public ResponseEntity<ErrorResponse> handleGeneric(Exception ex) {
         log.error("Unhandled exception", ex);
diff --git a/backend/src/test/java/org/raddatz/familienarchiv/controller/PersonControllerTest.java b/backend/src/test/java/org/raddatz/familienarchiv/controller/PersonControllerTest.java
index dbc9084c..e04ba664 100644
--- a/backend/src/test/java/org/raddatz/familienarchiv/controller/PersonControllerTest.java
+++ b/backend/src/test/java/org/raddatz/familienarchiv/controller/PersonControllerTest.java
@@ -2,6 +2,7 @@ package org.raddatz.familienarchiv.controller;
 
 import org.junit.jupiter.api.Test;
 import org.raddatz.familienarchiv.model.Document;
+import org.raddatz.familienarchiv.model.Person;
 import org.raddatz.familienarchiv.security.PermissionAspect;
 import org.raddatz.familienarchiv.service.CustomUserDetailsService;
 import org.raddatz.familienarchiv.service.DocumentService;
@@ -11,15 +12,20 @@ import org.springframework.boot.webmvc.test.autoconfigure.WebMvcTest;
 import org.raddatz.familienarchiv.config.SecurityConfig;
 import org.springframework.boot.autoconfigure.aop.AopAutoConfiguration;
 import org.springframework.context.annotation.Import;
+import org.springframework.http.MediaType;
 import org.springframework.security.test.context.support.WithMockUser;
 import org.springframework.test.context.bean.override.mockito.MockitoBean;
 import org.springframework.test.web.servlet.MockMvc;
 
 import java.util.Collections;
+import java.util.List;
 import java.util.UUID;
 
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.when;
-import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 @WebMvcTest(PersonController.class)
@@ -32,6 +38,101 @@ class PersonControllerTest {
     @MockitoBean DocumentService documentService;
     @MockitoBean CustomUserDetailsService customUserDetailsService;
 
+    // ─── GET /api/persons ─────────────────────────────────────────────────────
+
+    @Test
+    void getPersons_returns401_whenUnauthenticated() throws Exception {
+        mockMvc.perform(get("/api/persons"))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    @WithMockUser
+    void getPersons_returns200_withEmptyList() throws Exception {
+        when(personService.findAll(null)).thenReturn(Collections.emptyList());
+        mockMvc.perform(get("/api/persons"))
+                .andExpect(status().isOk());
+    }
+
+    @Test
+    @WithMockUser
+    void getPersons_delegatesQueryParam_toService() throws Exception {
+        Person person = Person.builder().id(UUID.randomUUID()).firstName("Hans").lastName("Müller").build();
+        when(personService.findAll("Hans")).thenReturn(List.of(person));
+
+        mockMvc.perform(get("/api/persons").param("q", "Hans"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$[0].firstName").value("Hans"));
+    }
+
+    // ─── GET /api/persons/{id} ────────────────────────────────────────────────
+
+    @Test
+    void getPerson_returns401_whenUnauthenticated() throws Exception {
+        mockMvc.perform(get("/api/persons/{id}", UUID.randomUUID()))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    @WithMockUser
+    void getPerson_returns200_whenFound() throws Exception {
+        UUID id = UUID.randomUUID();
+        Person person = Person.builder().id(id).firstName("Anna").lastName("Schmidt").build();
+        when(personService.getById(id)).thenReturn(person);
+
+        mockMvc.perform(get("/api/persons/{id}", id))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.firstName").value("Anna"));
+    }
+
+    // ─── GET /api/persons/{id}/correspondents ─────────────────────────────────
+
+    @Test
+    void getCorrespondents_returns401_whenUnauthenticated() throws Exception {
+        mockMvc.perform(get("/api/persons/{id}/correspondents", UUID.randomUUID()))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    @WithMockUser
+    void getCorrespondents_returns200_withoutFilter() throws Exception {
+        UUID personId = UUID.randomUUID();
+        when(personService.findCorrespondents(personId, null)).thenReturn(Collections.emptyList());
+
+        mockMvc.perform(get("/api/persons/{id}/correspondents", personId))
+                .andExpect(status().isOk());
+    }
+
+    @Test
+    @WithMockUser
+    void getCorrespondents_returns200_withFilter() throws Exception {
+        UUID personId = UUID.randomUUID();
+        Person correspondent = Person.builder().id(UUID.randomUUID()).firstName("Walter").lastName("Gruyter").build();
+        when(personService.findCorrespondents(personId, "Walter")).thenReturn(List.of(correspondent));
+
+        mockMvc.perform(get("/api/persons/{id}/correspondents", personId).param("q", "Walter"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$[0].firstName").value("Walter"));
+    }
+
+    // ─── GET /api/persons/{id}/documents ──────────────────────────────────────
+
+    @Test
+    void getPersonDocuments_returns401_whenUnauthenticated() throws Exception {
+        mockMvc.perform(get("/api/persons/{id}/documents", UUID.randomUUID()))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    @WithMockUser
+    void getPersonDocuments_returns200_whenAuthenticated() throws Exception {
+        UUID personId = UUID.randomUUID();
+        when(documentService.getDocumentsBySender(personId)).thenReturn(Collections.emptyList());
+
+        mockMvc.perform(get("/api/persons/{id}/documents", personId))
+                .andExpect(status().isOk());
+    }
+
     // ─── GET /api/persons/{id}/received-documents ─────────────────────────────
 
     @Test
@@ -49,4 +150,145 @@ class PersonControllerTest {
         mockMvc.perform(get("/api/persons/{id}/received-documents", personId))
                 .andExpect(status().isOk());
     }
+
+    // ─── POST /api/persons ────────────────────────────────────────────────────
+
+    @Test
+    void createPerson_returns401_whenUnauthenticated() throws Exception {
+        mockMvc.perform(post("/api/persons")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"firstName\":\"Hans\",\"lastName\":\"Müller\"}"))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    @WithMockUser
+    void createPerson_returns400_whenFirstNameIsMissing() throws Exception {
+        mockMvc.perform(post("/api/persons")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"lastName\":\"Müller\"}"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    @WithMockUser
+    void createPerson_returns400_whenFirstNameIsBlank() throws Exception {
+        mockMvc.perform(post("/api/persons")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"firstName\":\"  \",\"lastName\":\"Müller\"}"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    @WithMockUser
+    void createPerson_returns400_whenLastNameIsMissing() throws Exception {
+        mockMvc.perform(post("/api/persons")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"firstName\":\"Hans\"}"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    @WithMockUser
+    void createPerson_returns400_whenLastNameIsBlank() throws Exception {
+        mockMvc.perform(post("/api/persons")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"firstName\":\"Hans\",\"lastName\":\"  \"}"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    @WithMockUser
+    void createPerson_returns200_whenValid() throws Exception {
+        Person saved = Person.builder().id(UUID.randomUUID()).firstName("Hans").lastName("Müller").build();
+        when(personService.createPerson(eq("Hans"), eq("Müller"), any())).thenReturn(saved);
+
+        mockMvc.perform(post("/api/persons")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"firstName\":\"Hans\",\"lastName\":\"Müller\"}"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.firstName").value("Hans"));
+    }
+
+    // ─── PUT /api/persons/{id} ────────────────────────────────────────────────
+
+    @Test
+    void updatePerson_returns401_whenUnauthenticated() throws Exception {
+        mockMvc.perform(put("/api/persons/{id}", UUID.randomUUID())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"firstName\":\"Hans\",\"lastName\":\"Müller\"}"))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    @WithMockUser
+    void updatePerson_returns400_whenFirstNameIsBlank() throws Exception {
+        mockMvc.perform(put("/api/persons/{id}", UUID.randomUUID())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"firstName\":\"\",\"lastName\":\"Müller\"}"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    @WithMockUser
+    void updatePerson_returns400_whenLastNameIsNull() throws Exception {
+        mockMvc.perform(put("/api/persons/{id}", UUID.randomUUID())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"firstName\":\"Hans\"}"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    @WithMockUser
+    void updatePerson_returns200_whenValid() throws Exception {
+        UUID id = UUID.randomUUID();
+        Person updated = Person.builder().id(id).firstName("Hans").lastName("Müller").build();
+        when(personService.updatePerson(eq(id), any())).thenReturn(updated);
+
+        mockMvc.perform(put("/api/persons/{id}", id)
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"firstName\":\"Hans\",\"lastName\":\"Müller\"}"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.lastName").value("Müller"));
+    }
+
+    // ─── POST /api/persons/{id}/merge ─────────────────────────────────────────
+
+    @Test
+    void mergePerson_returns401_whenUnauthenticated() throws Exception {
+        mockMvc.perform(post("/api/persons/{id}/merge", UUID.randomUUID())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"targetPersonId\":\"" + UUID.randomUUID() + "\"}"))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    @WithMockUser
+    void mergePerson_returns400_whenTargetPersonIdIsMissing() throws Exception {
+        mockMvc.perform(post("/api/persons/{id}/merge", UUID.randomUUID())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{}"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    @WithMockUser
+    void mergePerson_returns400_whenTargetPersonIdIsBlank() throws Exception {
+        mockMvc.perform(post("/api/persons/{id}/merge", UUID.randomUUID())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"targetPersonId\":\"  \"}"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    @WithMockUser
+    void mergePerson_returns204_whenValid() throws Exception {
+        UUID sourceId = UUID.randomUUID();
+        UUID targetId = UUID.randomUUID();
+
+        mockMvc.perform(post("/api/persons/{id}/merge", sourceId)
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"targetPersonId\":\"" + targetId + "\"}"))
+                .andExpect(status().isNoContent());
+    }
 }
diff --git a/backend/src/test/java/org/raddatz/familienarchiv/repository/DocumentSpecificationsTest.java b/backend/src/test/java/org/raddatz/familienarchiv/repository/DocumentSpecificationsTest.java
new file mode 100644
index 00000000..ccdd3408
--- /dev/null
+++ b/backend/src/test/java/org/raddatz/familienarchiv/repository/DocumentSpecificationsTest.java
@@ -0,0 +1,252 @@
+package org.raddatz.familienarchiv.repository;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.raddatz.familienarchiv.PostgresContainerConfig;
+import org.raddatz.familienarchiv.config.FlywayConfig;
+import org.raddatz.familienarchiv.model.Document;
+import org.raddatz.familienarchiv.model.DocumentStatus;
+import org.raddatz.familienarchiv.model.Person;
+import org.raddatz.familienarchiv.model.Tag;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.jdbc.test.autoconfigure.AutoConfigureTestDatabase;
+import org.springframework.boot.data.jpa.test.autoconfigure.DataJpaTest;
+import org.springframework.context.annotation.Import;
+import org.springframework.data.jpa.domain.Specification;
+
+import java.time.LocalDate;
+import java.util.List;
+import java.util.Set;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.raddatz.familienarchiv.repository.DocumentSpecifications.*;
+
+@DataJpaTest
+@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
+@Import({PostgresContainerConfig.class, FlywayConfig.class})
+class DocumentSpecificationsTest {
+
+    @Autowired DocumentRepository documentRepository;
+    @Autowired PersonRepository personRepository;
+    @Autowired TagRepository tagRepository;
+
+    private Person sender;
+    private Person receiver;
+    private Document briefEarly;
+    private Document briefLate;
+    private Document photoDoc;
+
+    @BeforeEach
+    void setUp() {
+        documentRepository.deleteAll();
+        personRepository.deleteAll();
+        tagRepository.deleteAll();
+
+        sender   = personRepository.save(Person.builder().firstName("Walter").lastName("Müller").build());
+        receiver = personRepository.save(Person.builder().firstName("Anna").lastName("Schmidt").build());
+
+        Tag tagFamilie = tagRepository.save(Tag.builder().name("Familie").build());
+        Tag tagUrlaub  = tagRepository.save(Tag.builder().name("Urlaub").build());
+
+        briefEarly = documentRepository.save(Document.builder()
+                .title("Alter Brief")
+                .originalFilename("brief_early.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .documentDate(LocalDate.of(1940, 5, 1))
+                .transcription("Liebe Anna, ich schreibe dir aus dem Krieg")
+                .location("Berlin")
+                .sender(sender)
+                .receivers(Set.of(receiver))
+                .tags(Set.of(tagFamilie))
+                .build());
+
+        briefLate = documentRepository.save(Document.builder()
+                .title("Neuerer Brief")
+                .originalFilename("brief_late.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .documentDate(LocalDate.of(1960, 8, 15))
+                .sender(sender)
+                .tags(Set.of(tagUrlaub))
+                .build());
+
+        photoDoc = documentRepository.save(Document.builder()
+                .title("Familienfoto")
+                .originalFilename("familienfoto.jpg")
+                .status(DocumentStatus.PLACEHOLDER)
+                .build());
+    }
+
+    // ─── hasText ──────────────────────────────────────────────────────────────
+
+    @Test
+    void hasText_returnsAllDocuments_whenTextIsNull() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasText(null)));
+        assertThat(result).hasSize(3);
+    }
+
+    @Test
+    void hasText_returnsAllDocuments_whenTextIsBlank() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasText("   ")));
+        assertThat(result).hasSize(3);
+    }
+
+    @Test
+    void hasText_filtersOnTitle() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasText("familienfoto")));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Familienfoto");
+    }
+
+    @Test
+    void hasText_filtersOnOriginalFilename() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasText("brief_late")));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Neuerer Brief");
+    }
+
+    @Test
+    void hasText_filtersOnTranscription() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasText("schreibe dir")));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Alter Brief");
+    }
+
+    @Test
+    void hasText_filtersOnLocation() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasText("berlin")));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Alter Brief");
+    }
+
+    @Test
+    void hasText_isCaseInsensitive() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasText("BRIEF")));
+        assertThat(result).extracting(Document::getTitle).containsExactlyInAnyOrder("Alter Brief", "Neuerer Brief");
+    }
+
+    @Test
+    void hasText_returnsEmpty_whenNoMatch() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasText("xyznotexist")));
+        assertThat(result).isEmpty();
+    }
+
+    // ─── hasSender ────────────────────────────────────────────────────────────
+
+    @Test
+    void hasSender_returnsAllDocuments_whenPersonIdIsNull() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasSender(null)));
+        assertThat(result).hasSize(3);
+    }
+
+    @Test
+    void hasSender_filtersDocumentsBySender() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasSender(sender.getId())));
+        assertThat(result).extracting(Document::getTitle)
+                .containsExactlyInAnyOrder("Alter Brief", "Neuerer Brief");
+    }
+
+    @Test
+    void hasSender_returnsEmpty_whenSenderHasNoDocuments() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasSender(receiver.getId())));
+        assertThat(result).isEmpty();
+    }
+
+    // ─── hasReceiver ──────────────────────────────────────────────────────────
+
+    @Test
+    void hasReceiver_returnsAllDocuments_whenPersonIdIsNull() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasReceiver(null)));
+        assertThat(result).hasSize(3);
+    }
+
+    @Test
+    void hasReceiver_filtersDocumentsByReceiver() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasReceiver(receiver.getId())));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Alter Brief");
+    }
+
+    @Test
+    void hasReceiver_returnsEmpty_whenReceiverHasNoDocuments() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasReceiver(sender.getId())));
+        assertThat(result).isEmpty();
+    }
+
+    // ─── isBetween ────────────────────────────────────────────────────────────
+
+    @Test
+    void isBetween_returnsAllDocuments_whenBothDatesAreNull() {
+        List<Document> result = documentRepository.findAll(Specification.where(isBetween(null, null)));
+        assertThat(result).hasSize(3);
+    }
+
+    @Test
+    void isBetween_filtersByBothDates() {
+        List<Document> result = documentRepository.findAll(
+                Specification.where(isBetween(LocalDate.of(1939, 1, 1), LocalDate.of(1945, 12, 31))));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Alter Brief");
+    }
+
+    @Test
+    void isBetween_filtersByStartDateOnly() {
+        List<Document> result = documentRepository.findAll(
+                Specification.where(isBetween(LocalDate.of(1950, 1, 1), null)));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Neuerer Brief");
+    }
+
+    @Test
+    void isBetween_filtersByEndDateOnly() {
+        List<Document> result = documentRepository.findAll(
+                Specification.where(isBetween(null, LocalDate.of(1945, 12, 31))));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Alter Brief");
+    }
+
+    @Test
+    void isBetween_returnsEmpty_whenNoDatesInRange() {
+        List<Document> result = documentRepository.findAll(
+                Specification.where(isBetween(LocalDate.of(1970, 1, 1), LocalDate.of(1980, 12, 31))));
+        assertThat(result).isEmpty();
+    }
+
+    // ─── hasTags ──────────────────────────────────────────────────────────────
+
+    @Test
+    void hasTags_returnsAllDocuments_whenTagListIsNull() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasTags(null)));
+        assertThat(result).hasSize(3);
+    }
+
+    @Test
+    void hasTags_returnsAllDocuments_whenTagListIsEmpty() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasTags(List.of())));
+        assertThat(result).hasSize(3);
+    }
+
+    @Test
+    void hasTags_filtersDocumentsByTag() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasTags(List.of("Familie"))));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Alter Brief");
+    }
+
+    @Test
+    void hasTags_isCaseInsensitive() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasTags(List.of("familie"))));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Alter Brief");
+    }
+
+    @Test
+    void hasTags_requiresAllTagsToBePresent_andLogic() {
+        // briefEarly has "Familie" but not "Urlaub" — should be excluded
+        List<Document> result = documentRepository.findAll(
+                Specification.where(hasTags(List.of("Familie", "Urlaub"))));
+        assertThat(result).isEmpty();
+    }
+
+    @Test
+    void hasTags_skipsEmptyTagNames() {
+        // An empty string in the tag list should be ignored
+        List<Document> result = documentRepository.findAll(Specification.where(hasTags(List.of("  ", "Familie"))));
+        assertThat(result).extracting(Document::getTitle).containsExactly("Alter Brief");
+    }
+
+    @Test
+    void hasTags_returnsEmpty_whenTagDoesNotExist() {
+        List<Document> result = documentRepository.findAll(Specification.where(hasTags(List.of("Unbekannt"))));
+        assertThat(result).isEmpty();
+    }
+}
diff --git a/backend/src/test/java/org/raddatz/familienarchiv/repository/PersonRepositoryTest.java b/backend/src/test/java/org/raddatz/familienarchiv/repository/PersonRepositoryTest.java
index 8ed8fb09..7f81dd15 100644
--- a/backend/src/test/java/org/raddatz/familienarchiv/repository/PersonRepositoryTest.java
+++ b/backend/src/test/java/org/raddatz/familienarchiv/repository/PersonRepositoryTest.java
@@ -3,6 +3,8 @@ package org.raddatz.familienarchiv.repository;
 import org.junit.jupiter.api.Test;
 import org.raddatz.familienarchiv.PostgresContainerConfig;
 import org.raddatz.familienarchiv.config.FlywayConfig;
+import org.raddatz.familienarchiv.model.Document;
+import org.raddatz.familienarchiv.model.DocumentStatus;
 import org.raddatz.familienarchiv.model.Person;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.jdbc.test.autoconfigure.AutoConfigureTestDatabase;
@@ -11,6 +13,7 @@ import org.springframework.context.annotation.Import;
 
 import java.util.List;
 import java.util.Optional;
+import java.util.Set;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -22,6 +25,9 @@ class PersonRepositoryTest {
     @Autowired
     private PersonRepository personRepository;
 
+    @Autowired
+    private DocumentRepository documentRepository;
+
     // ─── save and findById ────────────────────────────────────────────────────
 
     @Test
@@ -133,4 +139,163 @@ class PersonRepositoryTest {
         assertThat(found).isPresent();
         assertThat(found.get().getFirstName()).isEqualTo("Maria");
     }
+
+    // ─── findCorrespondents ───────────────────────────────────────────────────
+
+    @Test
+    void findCorrespondents_returnsPersonsWhoSharedDocumentsWith() {
+        Person walter = personRepository.save(Person.builder().firstName("Walter").lastName("Müller").build());
+        Person anna   = personRepository.save(Person.builder().firstName("Anna").lastName("Schmidt").build());
+        Person clara  = personRepository.save(Person.builder().firstName("Clara").lastName("Cram").build());
+
+        // Walter sends to Anna (1 document)
+        documentRepository.save(Document.builder()
+                .title("Brief 1").originalFilename("brief1.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(walter).receivers(Set.of(anna)).build());
+
+        // Walter sends to Clara (2 documents — Clara should rank higher)
+        documentRepository.save(Document.builder()
+                .title("Brief 2").originalFilename("brief2.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(walter).receivers(Set.of(clara)).build());
+        documentRepository.save(Document.builder()
+                .title("Brief 3").originalFilename("brief3.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(walter).receivers(Set.of(clara)).build());
+
+        List<Person> correspondents = personRepository.findCorrespondents(walter.getId());
+
+        assertThat(correspondents).extracting(Person::getFirstName)
+                .containsExactly("Clara", "Anna"); // Clara ranks first (2 documents)
+    }
+
+    @Test
+    void findCorrespondents_returnsEmpty_whenPersonHasNoDocuments() {
+        Person solo = personRepository.save(Person.builder().firstName("Solo").lastName("Mensch").build());
+
+        List<Person> correspondents = personRepository.findCorrespondents(solo.getId());
+
+        assertThat(correspondents).isEmpty();
+    }
+
+    // ─── findCorrespondentsWithFilter ─────────────────────────────────────────
+
+    @Test
+    void findCorrespondentsWithFilter_returnsOnlyMatchingCorrespondents() {
+        Person walter = personRepository.save(Person.builder().firstName("Walter").lastName("Müller").build());
+        Person anna   = personRepository.save(Person.builder().firstName("Anna").lastName("Schmidt").build());
+        Person bernd  = personRepository.save(Person.builder().firstName("Bernd").lastName("Braun").build());
+
+        documentRepository.save(Document.builder()
+                .title("Brief an Anna").originalFilename("anna.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(walter).receivers(Set.of(anna)).build());
+        documentRepository.save(Document.builder()
+                .title("Brief an Bernd").originalFilename("bernd.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(walter).receivers(Set.of(bernd)).build());
+
+        List<Person> filtered = personRepository.findCorrespondentsWithFilter(walter.getId(), "Anna");
+
+        assertThat(filtered).extracting(Person::getFirstName).containsExactly("Anna");
+    }
+
+    @Test
+    void findCorrespondentsWithFilter_isCaseInsensitive() {
+        Person walter = personRepository.save(Person.builder().firstName("Walter").lastName("Müller").build());
+        Person anna   = personRepository.save(Person.builder().firstName("Anna").lastName("Schmidt").build());
+
+        documentRepository.save(Document.builder()
+                .title("Brief").originalFilename("brief.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(walter).receivers(Set.of(anna)).build());
+
+        List<Person> filtered = personRepository.findCorrespondentsWithFilter(walter.getId(), "schmidt");
+
+        assertThat(filtered).hasSize(1);
+        assertThat(filtered.get(0).getLastName()).isEqualTo("Schmidt");
+    }
+
+    // ─── reassignSender ───────────────────────────────────────────────────────
+
+    @Test
+    void reassignSender_updatesDocumentsSenderFromSourceToTarget() {
+        Person source = personRepository.save(Person.builder().firstName("Alt").lastName("Person").build());
+        Person target = personRepository.save(Person.builder().firstName("Neu").lastName("Person").build());
+
+        documentRepository.save(Document.builder()
+                .title("Brief").originalFilename("brief.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(source).build());
+
+        personRepository.reassignSender(source.getId(), target.getId());
+
+        List<Document> docs = documentRepository.findBySenderId(target.getId());
+        assertThat(docs).hasSize(1);
+        assertThat(documentRepository.findBySenderId(source.getId())).isEmpty();
+    }
+
+    // ─── insertMissingReceiverReference ──────────────────────────────────────
+
+    @Test
+    void insertMissingReceiverReference_addsTargetWhereSourceWasReceiver() {
+        Person source = personRepository.save(Person.builder().firstName("Alt").lastName("Person").build());
+        Person target = personRepository.save(Person.builder().firstName("Neu").lastName("Person").build());
+        Person sender = personRepository.save(Person.builder().firstName("Send").lastName("Er").build());
+
+        Document doc = documentRepository.save(Document.builder()
+                .title("Brief").originalFilename("brief.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(sender).receivers(Set.of(source)).build());
+
+        personRepository.insertMissingReceiverReference(source.getId(), target.getId());
+
+        Document reloaded = documentRepository.findById(doc.getId()).orElseThrow();
+        assertThat(reloaded.getReceivers())
+                .extracting(Person::getId)
+                .contains(target.getId());
+    }
+
+    @Test
+    void insertMissingReceiverReference_doesNotCreateDuplicate_whenTargetAlreadyReceiver() {
+        Person source = personRepository.save(Person.builder().firstName("Alt").lastName("Person").build());
+        Person target = personRepository.save(Person.builder().firstName("Neu").lastName("Person").build());
+        Person sender = personRepository.save(Person.builder().firstName("Send").lastName("Er").build());
+
+        // target is already a receiver together with source
+        Document doc = documentRepository.save(Document.builder()
+                .title("Brief").originalFilename("brief.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(sender).receivers(Set.of(source, target)).build());
+
+        personRepository.insertMissingReceiverReference(source.getId(), target.getId());
+
+        Document reloaded = documentRepository.findById(doc.getId()).orElseThrow();
+        long targetCount = reloaded.getReceivers().stream()
+                .filter(p -> p.getId().equals(target.getId())).count();
+        assertThat(targetCount).isEqualTo(1); // no duplicate
+    }
+
+    // ─── deleteReceiverReferences ─────────────────────────────────────────────
+
+    @Test
+    void deleteReceiverReferences_removesPersonFromAllDocumentReceivers() {
+        Person toDelete = personRepository.save(Person.builder().firstName("Weg").lastName("Person").build());
+        Person sender   = personRepository.save(Person.builder().firstName("Send").lastName("Er").build());
+
+        Document doc1 = documentRepository.save(Document.builder()
+                .title("Brief 1").originalFilename("b1.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(sender).receivers(Set.of(toDelete)).build());
+        Document doc2 = documentRepository.save(Document.builder()
+                .title("Brief 2").originalFilename("b2.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(sender).receivers(Set.of(toDelete)).build());
+
+        personRepository.deleteReceiverReferences(toDelete.getId());
+
+        assertThat(documentRepository.findById(doc1.getId()).orElseThrow().getReceivers()).isEmpty();
+        assertThat(documentRepository.findById(doc2.getId()).orElseThrow().getReceivers()).isEmpty();
+    }
 }