diff --git a/backend/src/test/java/org/raddatz/familienarchiv/service/TranscriptionServiceTest.java b/backend/src/test/java/org/raddatz/familienarchiv/service/TranscriptionServiceTest.java
new file mode 100644
index 00000000..efc6de6a
--- /dev/null
+++ b/backend/src/test/java/org/raddatz/familienarchiv/service/TranscriptionServiceTest.java
@@ -0,0 +1,247 @@
+package org.raddatz.familienarchiv.service;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.raddatz.familienarchiv.dto.CreateAnnotationDTO;
+import org.raddatz.familienarchiv.dto.CreateTranscriptionBlockDTO;
+import org.raddatz.familienarchiv.dto.ReorderTranscriptionBlocksDTO;
+import org.raddatz.familienarchiv.dto.UpdateTranscriptionBlockDTO;
+import org.raddatz.familienarchiv.exception.DomainException;
+import org.raddatz.familienarchiv.model.Document;
+import org.raddatz.familienarchiv.model.DocumentAnnotation;
+import org.raddatz.familienarchiv.model.TranscriptionBlock;
+import org.raddatz.familienarchiv.model.TranscriptionBlockVersion;
+import org.raddatz.familienarchiv.repository.AnnotationRepository;
+import org.raddatz.familienarchiv.repository.TranscriptionBlockRepository;
+import org.raddatz.familienarchiv.repository.TranscriptionBlockVersionRepository;
+
+import java.util.List;
+import java.util.Optional;
+import java.util.UUID;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+import static org.springframework.http.HttpStatus.NOT_FOUND;
+
+@ExtendWith(MockitoExtension.class)
+class TranscriptionServiceTest {
+
+    @Mock TranscriptionBlockRepository blockRepository;
+    @Mock TranscriptionBlockVersionRepository versionRepository;
+    @Mock AnnotationRepository annotationRepository;
+    @Mock AnnotationService annotationService;
+    @Mock DocumentService documentService;
+    @InjectMocks TranscriptionService transcriptionService;
+
+    // ─── getBlock ────────────────────────────────────────────────────────────────
+
+    @Test
+    void getBlock_throwsNotFound_whenBlockDoesNotExist() {
+        UUID docId = UUID.randomUUID();
+        UUID blockId = UUID.randomUUID();
+        when(blockRepository.findByIdAndDocumentId(blockId, docId)).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> transcriptionService.getBlock(docId, blockId))
+                .isInstanceOf(DomainException.class)
+                .satisfies(e -> assertThat(((DomainException) e).getStatus()).isEqualTo(NOT_FOUND));
+    }
+
+    @Test
+    void getBlock_returnsBlock_whenExists() {
+        UUID docId = UUID.randomUUID();
+        UUID blockId = UUID.randomUUID();
+        TranscriptionBlock block = TranscriptionBlock.builder()
+                .id(blockId).documentId(docId).text("hello").build();
+        when(blockRepository.findByIdAndDocumentId(blockId, docId)).thenReturn(Optional.of(block));
+
+        TranscriptionBlock result = transcriptionService.getBlock(docId, blockId);
+
+        assertThat(result).isEqualTo(block);
+    }
+
+    // ─── createBlock ─────────────────────────────────────────────────────────────
+
+    @Test
+    void createBlock_createsAnnotationAndBlockAndVersion() {
+        UUID docId = UUID.randomUUID();
+        UUID userId = UUID.randomUUID();
+        UUID annotId = UUID.randomUUID();
+
+        Document doc = Document.builder().id(docId).fileHash("hash123").build();
+        when(documentService.getDocumentById(docId)).thenReturn(doc);
+
+        DocumentAnnotation annotation = DocumentAnnotation.builder().id(annotId).build();
+        when(annotationService.createAnnotation(eq(docId), any(CreateAnnotationDTO.class), eq(userId), eq("hash123")))
+                .thenReturn(annotation);
+
+        when(blockRepository.countByDocumentId(docId)).thenReturn(0);
+        when(blockRepository.save(any())).thenAnswer(inv -> {
+            TranscriptionBlock b = inv.getArgument(0);
+            b.setId(UUID.randomUUID());
+            return b;
+        });
+
+        CreateTranscriptionBlockDTO dto = new CreateTranscriptionBlockDTO(1, 0.1, 0.2, 0.3, 0.4, "hello", null);
+
+        TranscriptionBlock result = transcriptionService.createBlock(docId, dto, userId);
+
+        assertThat(result.getAnnotationId()).isEqualTo(annotId);
+        assertThat(result.getText()).isEqualTo("hello");
+        assertThat(result.getSortOrder()).isZero();
+        assertThat(result.getCreatedBy()).isEqualTo(userId);
+        verify(versionRepository).save(any(TranscriptionBlockVersion.class));
+    }
+
+    // ─── updateBlock ─────────────────────────────────────────────────────────────
+
+    @Test
+    void updateBlock_updatesTextAndSavesVersion() {
+        UUID docId = UUID.randomUUID();
+        UUID blockId = UUID.randomUUID();
+        UUID userId = UUID.randomUUID();
+
+        TranscriptionBlock block = TranscriptionBlock.builder()
+                .id(blockId).documentId(docId).text("old").build();
+        when(blockRepository.findByIdAndDocumentId(blockId, docId)).thenReturn(Optional.of(block));
+        when(blockRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
+
+        UpdateTranscriptionBlockDTO dto = new UpdateTranscriptionBlockDTO("new text", null);
+
+        TranscriptionBlock result = transcriptionService.updateBlock(docId, blockId, dto, userId);
+
+        assertThat(result.getText()).isEqualTo("new text");
+        assertThat(result.getUpdatedBy()).isEqualTo(userId);
+        verify(versionRepository).save(any(TranscriptionBlockVersion.class));
+    }
+
+    @Test
+    void updateBlock_updatesLabel_whenProvided() {
+        UUID docId = UUID.randomUUID();
+        UUID blockId = UUID.randomUUID();
+
+        TranscriptionBlock block = TranscriptionBlock.builder()
+                .id(blockId).documentId(docId).text("text").label("old label").build();
+        when(blockRepository.findByIdAndDocumentId(blockId, docId)).thenReturn(Optional.of(block));
+        when(blockRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
+
+        UpdateTranscriptionBlockDTO dto = new UpdateTranscriptionBlockDTO("text", "Anrede");
+
+        TranscriptionBlock result = transcriptionService.updateBlock(docId, blockId, dto, UUID.randomUUID());
+
+        assertThat(result.getLabel()).isEqualTo("Anrede");
+    }
+
+    // ─── deleteBlock ─────────────────────────────────────────────────────────────
+
+    @Test
+    void deleteBlock_deletesBlockAndAnnotation() {
+        UUID docId = UUID.randomUUID();
+        UUID blockId = UUID.randomUUID();
+        UUID annotId = UUID.randomUUID();
+
+        TranscriptionBlock block = TranscriptionBlock.builder()
+                .id(blockId).documentId(docId).annotationId(annotId).build();
+        when(blockRepository.findByIdAndDocumentId(blockId, docId)).thenReturn(Optional.of(block));
+
+        transcriptionService.deleteBlock(docId, blockId);
+
+        verify(blockRepository).delete(block);
+        verify(blockRepository).flush();
+        verify(annotationRepository).deleteById(annotId);
+    }
+
+    @Test
+    void deleteBlock_throwsNotFound_whenBlockMissing() {
+        UUID docId = UUID.randomUUID();
+        UUID blockId = UUID.randomUUID();
+        when(blockRepository.findByIdAndDocumentId(blockId, docId)).thenReturn(Optional.empty());
+
+        assertThatThrownBy(() -> transcriptionService.deleteBlock(docId, blockId))
+                .isInstanceOf(DomainException.class)
+                .satisfies(e -> assertThat(((DomainException) e).getStatus()).isEqualTo(NOT_FOUND));
+    }
+
+    // ─── reorderBlocks ───────────────────────────────────────────────────────────
+
+    @Test
+    void reorderBlocks_updatesSortOrder() {
+        UUID docId = UUID.randomUUID();
+        UUID id1 = UUID.randomUUID();
+        UUID id2 = UUID.randomUUID();
+
+        TranscriptionBlock block1 = TranscriptionBlock.builder()
+                .id(id1).documentId(docId).sortOrder(0).build();
+        TranscriptionBlock block2 = TranscriptionBlock.builder()
+                .id(id2).documentId(docId).sortOrder(1).build();
+
+        when(blockRepository.findByIdAndDocumentId(id2, docId)).thenReturn(Optional.of(block2));
+        when(blockRepository.findByIdAndDocumentId(id1, docId)).thenReturn(Optional.of(block1));
+        when(blockRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
+        when(blockRepository.findByDocumentIdOrderBySortOrderAsc(docId)).thenReturn(List.of(block2, block1));
+
+        ReorderTranscriptionBlocksDTO dto = new ReorderTranscriptionBlocksDTO(List.of(id2, id1));
+
+        transcriptionService.reorderBlocks(docId, dto);
+
+        assertThat(block2.getSortOrder()).isZero();
+        assertThat(block1.getSortOrder()).isEqualTo(1);
+    }
+
+    // ─── getBlockHistory ─────────────────────────────────────────────────────────
+
+    @Test
+    void getBlockHistory_returnsVersionsForBlock() {
+        UUID docId = UUID.randomUUID();
+        UUID blockId = UUID.randomUUID();
+
+        TranscriptionBlock block = TranscriptionBlock.builder()
+                .id(blockId).documentId(docId).build();
+        when(blockRepository.findByIdAndDocumentId(blockId, docId)).thenReturn(Optional.of(block));
+
+        TranscriptionBlockVersion v = TranscriptionBlockVersion.builder()
+                .id(UUID.randomUUID()).blockId(blockId).text("ver1").build();
+        when(versionRepository.findByBlockIdOrderByChangedAtDesc(blockId)).thenReturn(List.of(v));
+
+        List<TranscriptionBlockVersion> result = transcriptionService.getBlockHistory(docId, blockId);
+
+        assertThat(result).containsExactly(v);
+    }
+
+    // ─── sanitizeText ────────────────────────────────────────────────────────────
+
+    @Test
+    void sanitizeText_returnsEmptyString_forNull() {
+        assertThat(transcriptionService.sanitizeText(null)).isEmpty();
+    }
+
+    @Test
+    void sanitizeText_truncatesAtMaxLength() {
+        String longText = "a".repeat(15_000);
+        String result = transcriptionService.sanitizeText(longText);
+        assertThat(result).hasSize(10_000);
+    }
+
+    @Test
+    void sanitizeText_preservesPlainText() {
+        assertThat(transcriptionService.sanitizeText("Liebe Mutter,")).isEqualTo("Liebe Mutter,");
+    }
+
+    // ─── listBlocks ──────────────────────────────────────────────────────────────
+
+    @Test
+    void listBlocks_returnsBlocksOrderedBySortOrder() {
+        UUID docId = UUID.randomUUID();
+        TranscriptionBlock b = TranscriptionBlock.builder()
+                .id(UUID.randomUUID()).documentId(docId).sortOrder(0).build();
+        when(blockRepository.findByDocumentIdOrderBySortOrderAsc(docId)).thenReturn(List.of(b));
+
+        assertThat(transcriptionService.listBlocks(docId)).containsExactly(b);
+    }
+}