diff --git a/internal/sync/queue.go b/internal/sync/queue.go
new file mode 100644
index 0000000..981a9d8
--- /dev/null
+++ b/internal/sync/queue.go
@@ -0,0 +1,431 @@
+package sync
+
+import (
+	"bookmann/internal/database"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+const (
+	SyncTypeProgress  = "progress"
+	SyncTypeNote      = "note"
+	SyncTypeHighlight = "highlight"
+	SyncTypeBookmark  = "bookmark"
+)
+
+const (
+	SyncStatusPending    = "pending"
+	SyncStatusProcessing = "processing"
+	SyncStatusCompleted  = "completed"
+	SyncStatusFailed     = "failed"
+)
+
+const (
+	PriorityUserInitiated  = 1
+	PriorityBookCompletion = 2
+	PriorityCriticalNote   = 3
+	PriorityPageTurn       = 5
+	PriorityCheckpoint     = 7
+	PriorityBackgroundSync = 10
+)
+
+type SyncQueueProcessor struct {
+	db           *database.Queries
+	progressChan chan *ProgressUpdate
+	interval     time.Duration
+	batchSize    int
+}
+
+type ProgressUpdate struct {
+	DeviceID    pgtype.UUID
+	MediaItemID pgtype.UUID
+	UserID      pgtype.UUID
+	Percentage  float64
+	Epubcfi     *string
+	Chapter     *int
+	Character   *int64
+	Page        *int
+	TotalPages  *int
+	Source      string
+	SyncMode    string
+}
+
+type SyncQueueItem struct {
+	ID           pgtype.UUID
+	DeviceID     pgtype.UUID
+	MediaItemID  pgtype.UUID
+	SyncType     string
+	SyncData     []byte
+	Priority     int32
+	Attempts     int32
+	MaxAttempts  int32
+	Status       string
+	ErrorMessage *string
+	CreatedAt    time.Time
+	ProcessedAt  *time.Time
+}
+
+func NewSyncQueueProcessor(db *database.Queries) *SyncQueueProcessor {
+	return &SyncQueueProcessor{
+		db:           db,
+		progressChan: make(chan *ProgressUpdate, 100),
+		interval:     5 * time.Second,
+		batchSize:    50,
+	}
+}
+
+func (p *SyncQueueProcessor) Start(ctx context.Context) {
+	log.Printf("Starting sync queue processor (interval: %v, batch: %d)", p.interval, p.batchSize)
+
+	ticker := time.NewTicker(p.interval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			log.Println("Sync queue processor stopped")
+			return
+		case update := <-p.progressChan:
+			p.enqueueProgressUpdate(ctx, update)
+		case <-ticker.C:
+			p.processQueue(ctx)
+		}
+	}
+}
+
+func (p *SyncQueueProcessor) EnqueueProgress(update *ProgressUpdate) error {
+	select {
+	case p.progressChan <- update:
+		return nil
+	default:
+		return fmt.Errorf("progress channel is full")
+	}
+}
+
+func (p *SyncQueueProcessor) enqueueProgressUpdate(ctx context.Context, update *ProgressUpdate) {
+	syncData := map[string]interface{}{
+		"percentage": update.Percentage,
+		"source":     update.Source,
+		"timestamp":  time.Now().Format(time.RFC3339),
+	}
+
+	if update.Epubcfi != nil {
+		syncData["epubcfi"] = *update.Epubcfi
+	}
+	if update.Chapter != nil {
+		syncData["chapter"] = *update.Chapter
+	}
+	if update.Character != nil {
+		syncData["character"] = *update.Character
+	}
+	if update.Page != nil {
+		syncData["page"] = *update.Page
+	}
+	if update.TotalPages != nil {
+		syncData["total_pages"] = *update.TotalPages
+	}
+
+	syncDataJSON, err := json.Marshal(syncData)
+	if err != nil {
+		log.Printf("Failed to marshal sync data: %v", err)
+		return
+	}
+
+	priority := PriorityPageTurn
+	if update.SyncMode == "checkpoint" {
+		priority = PriorityCheckpoint
+	} else if update.Percentage >= 0.99 {
+		priority = PriorityBookCompletion
+	}
+
+	maxAttempts := int32(3)
+	if update.SyncMode == "immediate" {
+		maxAttempts = 5
+	}
+
+	_, err = p.db.CreateSyncQueueItem(ctx, database.CreateSyncQueueItemParams{
+		DeviceID:    update.DeviceID,
+		MediaItemID: update.MediaItemID,
+		SyncType:    SyncTypeProgress,
+		SyncData:    syncDataJSON,
+		Priority:    pgtype.Int4{Int32: int32(priority), Valid: true},
+		MaxAttempts: pgtype.Int4{Int32: maxAttempts, Valid: true},
+		Status:      pgtype.Text{String: SyncStatusPending, Valid: true},
+	})
+
+	if err != nil {
+		log.Printf("Failed to create sync queue item: %v", err)
+	}
+}
+
+func (p *SyncQueueProcessor) processQueue(ctx context.Context) {
+	items := p.getPendingItems(ctx)
+
+	if len(items) == 0 {
+		p.checkStuckItems(ctx)
+		return
+	}
+
+	log.Printf("Processing %d sync queue items", len(items))
+
+	for _, item := range items {
+		select {
+		case <-ctx.Done():
+			return
+		default:
+			p.processItem(ctx, item)
+		}
+	}
+}
+
+func (p *SyncQueueProcessor) getPendingItems(ctx context.Context) []SyncQueueItem {
+	var allItems []SyncQueueItem
+
+	var offset int32 = 0
+	batchSize := int32(p.batchSize)
+	for {
+		dbItems, err := p.db.ListPendingSyncQueueItems(ctx, database.ListPendingSyncQueueItemsParams{
+			DeviceID: pgtype.UUID{Valid: false},
+			Limit:    batchSize,
+		})
+		if err != nil {
+			log.Printf("Error listing pending items: %v", err)
+			break
+		}
+
+		if len(dbItems) == 0 {
+			break
+		}
+
+		for _, item := range dbItems {
+			if item.Status.String == SyncStatusPending {
+				allItems = append(allItems, dbItemToSyncQueueItem(item))
+			}
+		}
+
+		if int32(len(dbItems)) < batchSize {
+			break
+		}
+
+		offset += batchSize
+	}
+
+	return allItems
+}
+
+func (p *SyncQueueProcessor) checkStuckItems(ctx context.Context) {
+	items, err := p.db.GetStuckSyncQueueItems(ctx)
+	if err != nil {
+		return
+	}
+
+	for _, item := range items {
+		if item.Attempts.Int32 < item.MaxAttempts.Int32 {
+			log.Printf("Resetting stuck queue item %s", item.ID.Bytes)
+			_, err := p.db.UpdateSyncQueueItemStatus(ctx, database.UpdateSyncQueueItemStatusParams{
+				ID:           item.ID,
+				Status:       pgtype.Text{String: SyncStatusPending, Valid: true},
+				ErrorMessage: pgtype.Text{String: "Item was stuck in processing state", Valid: true},
+			})
+			if err != nil {
+				log.Printf("Failed to reset stuck item: %v", err)
+			}
+		}
+	}
+}
+
+func (p *SyncQueueProcessor) processItem(ctx context.Context, item SyncQueueItem) {
+	_, err := p.db.UpdateSyncQueueItemStatus(ctx, database.UpdateSyncQueueItemStatusParams{
+		ID:           item.ID,
+		Status:       pgtype.Text{String: SyncStatusProcessing, Valid: true},
+		ErrorMessage: pgtype.Text{},
+	})
+	if err != nil {
+		log.Printf("Failed to update item status to processing: %v", err)
+		return
+	}
+
+	var syncData map[string]interface{}
+	err = json.Unmarshal(item.SyncData, &syncData)
+	if err != nil {
+		log.Printf("Failed to unmarshal sync data: %v", err)
+		p.markItemFailed(ctx, item, fmt.Sprintf("Invalid sync data: %v", err))
+		return
+	}
+
+	err = p.executeSync(ctx, item, syncData)
+	if err != nil {
+		log.Printf("Sync failed for item %s: %v", item.ID.Bytes, err)
+
+		if item.Attempts >= item.MaxAttempts {
+			p.markItemFailed(ctx, item, fmt.Sprintf("Max attempts reached: %v", err))
+		} else {
+			nextRetry := p.calculateNextRetry(item.Attempts)
+			log.Printf("Scheduling retry for item %s at %v (attempt %d/%d)",
+				item.ID.Bytes, nextRetry, item.Attempts+1, item.MaxAttempts)
+
+			p.markItemPending(ctx, item, fmt.Sprintf("Will retry: %v", err))
+		}
+		return
+	}
+
+	_, err = p.db.UpdateSyncQueueItemStatus(ctx, database.UpdateSyncQueueItemStatusParams{
+		ID:           item.ID,
+		Status:       pgtype.Text{String: SyncStatusCompleted, Valid: true},
+		ErrorMessage: pgtype.Text{},
+	})
+	if err != nil {
+		log.Printf("Failed to mark item as completed: %v", err)
+	}
+
+	log.Printf("Successfully processed sync queue item %s", item.ID.Bytes)
+}
+
+func (p *SyncQueueProcessor) executeSync(ctx context.Context, item SyncQueueItem, syncData map[string]interface{}) error {
+	device, err := p.db.GetDevice(ctx, item.DeviceID)
+	if err != nil {
+		return fmt.Errorf("device not found: %w", err)
+	}
+
+	switch item.SyncType {
+	case SyncTypeProgress:
+		return p.syncProgress(ctx, device.UserID, item.MediaItemID, syncData)
+	case SyncTypeNote:
+		return p.syncNote(ctx, device.UserID, item.MediaItemID, syncData)
+	case SyncTypeHighlight:
+		return p.syncHighlight(ctx, device.UserID, item.MediaItemID, syncData)
+	default:
+		return fmt.Errorf("unsupported sync type: %s", item.SyncType)
+	}
+}
+
+func (p *SyncQueueProcessor) syncProgress(ctx context.Context, userID pgtype.UUID, mediaItemID pgtype.UUID, syncData map[string]interface{}) error {
+	percentage, ok := syncData["percentage"].(float64)
+	if !ok {
+		return fmt.Errorf("missing percentage in sync data")
+	}
+
+	var epubcfi pgtype.Text
+	if v, ok := syncData["epubcfi"].(string); ok {
+		epubcfi = pgtype.Text{String: v, Valid: true}
+	}
+
+	var chapter pgtype.Int4
+	if v, ok := syncData["chapter"].(float64); ok {
+		chapter = pgtype.Int4{Int32: int32(v), Valid: true}
+	}
+
+	var characterOffset pgtype.Int8
+	if v, ok := syncData["character"].(float64); ok {
+		characterOffset = pgtype.Int8{Int64: int64(v), Valid: true}
+	}
+
+	var currentPage pgtype.Int4
+	if v, ok := syncData["page"].(float64); ok {
+		currentPage = pgtype.Int4{Int32: int32(v), Valid: true}
+	}
+
+	var totalPages pgtype.Int4
+	if v, ok := syncData["total_pages"].(float64); ok {
+		totalPages = pgtype.Int4{Int32: int32(v), Valid: true}
+	}
+
+	source := "queue"
+	if v, ok := syncData["source"].(string); ok {
+		source = v
+	}
+
+	_, err := p.db.UpdateUniversalProgress(ctx, database.UpdateUniversalProgressParams{
+		MediaItemID:     mediaItemID,
+		UserID:          userID,
+		Percentage:      pgtype.Float8{Float64: percentage, Valid: true},
+		Epubcfi:         epubcfi,
+		Chapter:         chapter,
+		ChapterProgress: pgtype.Float8{Float64: percentage, Valid: true},
+		CharacterOffset: characterOffset,
+		CurrentPage:     currentPage,
+		TotalPages:      totalPages,
+		LastSyncDevice:  pgtype.Text{String: source, Valid: true},
+		LastSyncSource:  pgtype.Text{String: source, Valid: true},
+		ViewportX:       pgtype.Float8{},
+		ScrollPositionX: pgtype.Float8{},
+		ScrollPositionY: pgtype.Float8{},
+		PanelNumber:     pgtype.Int4{},
+		ReadingMode:     pgtype.Text{},
+		ZoomLevel:       pgtype.Float8{},
+	})
+
+	return err
+}
+
+func (p *SyncQueueProcessor) syncNote(ctx context.Context, userID pgtype.UUID, mediaItemID pgtype.UUID, syncData map[string]interface{}) error {
+	return fmt.Errorf("note sync not yet implemented")
+}
+
+func (p *SyncQueueProcessor) syncHighlight(ctx context.Context, userID pgtype.UUID, mediaItemID pgtype.UUID, syncData map[string]interface{}) error {
+	return fmt.Errorf("highlight sync not yet implemented")
+}
+
+func (p *SyncQueueProcessor) markItemFailed(ctx context.Context, item SyncQueueItem, errMsg string) {
+	_, err := p.db.UpdateSyncQueueItemStatus(ctx, database.UpdateSyncQueueItemStatusParams{
+		ID:           item.ID,
+		Status:       pgtype.Text{String: SyncStatusFailed, Valid: true},
+		ErrorMessage: pgtype.Text{String: errMsg, Valid: true},
+	})
+	if err != nil {
+		log.Printf("Failed to mark item as failed: %v", err)
+	}
+}
+
+func (p *SyncQueueProcessor) markItemPending(ctx context.Context, item SyncQueueItem, errMsg string) {
+	_, err := p.db.UpdateSyncQueueItemStatus(ctx, database.UpdateSyncQueueItemStatusParams{
+		ID:           item.ID,
+		Status:       pgtype.Text{String: SyncStatusPending, Valid: true},
+		ErrorMessage: pgtype.Text{String: errMsg, Valid: true},
+	})
+	if err != nil {
+		log.Printf("Failed to mark item as pending: %v", err)
+	}
+}
+
+func (p *SyncQueueProcessor) calculateNextRetry(attempts int32) time.Time {
+	switch attempts {
+	case 0:
+		return time.Now()
+	case 1:
+		return time.Now().Add(1 * time.Minute)
+	case 2:
+		return time.Now().Add(5 * time.Minute)
+	case 3:
+		return time.Now().Add(15 * time.Minute)
+	case 4:
+		return time.Now().Add(1 * time.Hour)
+	default:
+		return time.Now().Add(24 * time.Hour)
+	}
+}
+
+func (p *SyncQueueProcessor) GetQueueStats(ctx context.Context, deviceID pgtype.UUID) (database.GetSyncQueueStatsRow, error) {
+	return p.db.GetSyncQueueStats(ctx, deviceID)
+}
+
+func dbItemToSyncQueueItem(item database.SyncQueue) SyncQueueItem {
+	return SyncQueueItem{
+		ID:           item.ID,
+		DeviceID:     item.DeviceID,
+		MediaItemID:  item.MediaItemID,
+		SyncType:     item.SyncType,
+		Priority:     item.Priority.Int32,
+		Attempts:     item.Attempts.Int32,
+		MaxAttempts:  item.MaxAttempts.Int32,
+		Status:       item.Status.String,
+		ErrorMessage: (*string)(&item.ErrorMessage.String),
+		CreatedAt:    item.CreatedAt.Time,
+		ProcessedAt:  (*time.Time)(&item.ProcessedAt.Time),
+	}
+}
diff --git a/internal/sync/queue_test.go b/internal/sync/queue_test.go
new file mode 100644
index 0000000..c2fc4bc
--- /dev/null
+++ b/internal/sync/queue_test.go
@@ -0,0 +1,137 @@
+package sync
+
+import (
+	"bookmann/internal/database"
+	"context"
+	"encoding/json"
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgtype"
+	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSyncQueueProcessor_EnqueueProgress(t *testing.T) {
+	ctx := context.Background()
+	db := setupTestDB(t)
+	defer teardownTestDB(t, db)
+
+	processor := NewSyncQueueProcessor(db)
+
+	userID := pgtype.UUID{Bytes: uuid.New(), Valid: true}
+	deviceID := pgtype.UUID{Bytes: uuid.New(), Valid: true}
+	mediaItemID := pgtype.UUID{Bytes: uuid.New(), Valid: true}
+
+	percentage := 0.45
+	chapter := 3
+	update := &ProgressUpdate{
+		DeviceID:    deviceID,
+		MediaItemID: mediaItemID,
+		UserID:      userID,
+		Percentage:  percentage,
+		Chapter:     &chapter,
+		Source:      "koreader",
+		SyncMode:    "immediate",
+	}
+
+	err := processor.EnqueueProgress(update)
+	require.NoError(t, err, "should enqueue progress update")
+
+	items, err := db.ListPendingSyncQueueItems(ctx, database.ListPendingSyncQueueItemsParams{
+		DeviceID: deviceID,
+		Limit:    10,
+	})
+	require.NoError(t, err)
+	assert.Len(t, items, 1, "should have one queue item")
+
+	item := items[0]
+	assert.Equal(t, "progress", item.SyncType)
+	assert.Equal(t, SyncStatusPending, item.Status.String)
+	assert.Equal(t, int32(PriorityPageTurn), item.Priority.Int32)
+
+	var syncData map[string]interface{}
+	err = json.Unmarshal(item.SyncData, &syncData)
+	require.NoError(t, err)
+	assert.Equal(t, percentage, syncData["percentage"])
+	assert.Equal(t, "koreader", syncData["source"])
+}
+
+func TestCalculateNextRetry(t *testing.T) {
+	processor := &SyncQueueProcessor{}
+
+	tests := []struct {
+		name     string
+		attempts int32
+		minDelay time.Duration
+		maxDelay time.Duration
+	}{
+		{"Attempt 0", 0, 0, 1 * time.Second},
+		{"Attempt 1", 1, 59 * time.Second, 61 * time.Second},
+		{"Attempt 2", 2, 4*time.Minute + 59*time.Second, 5*time.Minute + 1*time.Second},
+		{"Attempt 3", 3, 14*time.Minute + 59*time.Second, 15*time.Minute + 1*time.Second},
+		{"Attempt 4", 4, 59*time.Minute + 59*time.Second, 60*time.Minute + 1*time.Second},
+		{"Attempt 5", 5, 23*time.Hour + 59*time.Minute, 24*time.Hour + 1*time.Minute},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			nextRetry := processor.calculateNextRetry(tt.attempts)
+			delay := nextRetry.Sub(time.Now())
+
+			assert.GreaterOrEqual(t, delay, tt.minDelay, "delay should be at least minDelay")
+			assert.LessOrEqual(t, delay, tt.maxDelay, "delay should be at most maxDelay")
+		})
+	}
+}
+
+func TestSyncTypeConstants(t *testing.T) {
+	assert.Equal(t, "progress", SyncTypeProgress)
+	assert.Equal(t, "note", SyncTypeNote)
+	assert.Equal(t, "highlight", SyncTypeHighlight)
+	assert.Equal(t, "bookmark", SyncTypeBookmark)
+}
+
+func TestSyncStatusConstants(t *testing.T) {
+	assert.Equal(t, "pending", SyncStatusPending)
+	assert.Equal(t, "processing", SyncStatusProcessing)
+	assert.Equal(t, "completed", SyncStatusCompleted)
+	assert.Equal(t, "failed", SyncStatusFailed)
+}
+
+func TestPriorityConstants(t *testing.T) {
+	assert.Equal(t, int32(1), PriorityUserInitiated)
+	assert.Equal(t, int32(2), PriorityBookCompletion)
+	assert.Equal(t, int32(3), PriorityCriticalNote)
+	assert.Equal(t, int32(5), PriorityPageTurn)
+	assert.Equal(t, int32(7), PriorityCheckpoint)
+	assert.Equal(t, int32(10), PriorityBackgroundSync)
+}
+
+func setupTestDB(t *testing.T) *database.Queries {
+	ctx := context.Background()
+
+	dbURL := "postgresql://postgres:postgres@localhost:5432/bookmann?sslmode=disable"
+	dbPool, err := pgxpool.New(ctx, dbURL)
+	require.NoError(t, err, "Failed to connect to test database")
+
+	db := database.New(dbPool)
+
+	t.Cleanup(func() {
+		_, _ = dbPool.Exec(ctx, "DELETE FROM sync_queue WHERE true")
+		_, _ = dbPool.Exec(ctx, "DELETE FROM reading_progress WHERE true")
+		_, _ = dbPool.Exec(ctx, "DELETE FROM media_items WHERE title LIKE 'Test %'")
+		_, _ = dbPool.Exec(ctx, "DELETE FROM libraries WHERE name LIKE 'Test %'")
+		_, _ = dbPool.Exec(ctx, "DELETE FROM devices WHERE device_name LIKE 'Test %'")
+		_, _ = dbPool.Exec(ctx, "DELETE FROM users WHERE email LIKE 'test%'")
+		dbPool.Close()
+	})
+
+	return db
+}
+
+func teardownTestDB(t *testing.T, db *database.Queries) {
+	// Cleanup is handled in setupTestDB via t.Cleanup
+}