diff --git a/graph2/resolvers/log.go b/graph2/resolvers/log.go
index 2e73ce7..7c996a2 100644
--- a/graph2/resolvers/log.go
+++ b/graph2/resolvers/log.go
@@ -62,6 +62,12 @@ func (r *mutationResolver) SplitLog(ctx context.Context, input graphcore.LogSpli
 	return r.s.Logs.SplitLog(ctx, input.LogID, input.StartPostID)
 }
 
+func (r *mutationResolver) MergeLog(ctx context.Context, input graphcore.LogMergeInput) (*models.Log, error) {
+	removeAfter := input.RemoveAfter != nil && *input.RemoveAfter
+
+	return r.s.Logs.MergeLogs(ctx, input.TargetLogID, input.SourceLogID, removeAfter)
+}
+
 func (r *mutationResolver) EditLog(ctx context.Context, input graphcore.LogEditInput) (*models.Log, error) {
 	update := models.LogUpdate{
 		Open:        input.Open,
diff --git a/graph2/schema/root.gql b/graph2/schema/root.gql
index ef79997..97146d6 100644
--- a/graph2/schema/root.gql
+++ b/graph2/schema/root.gql
@@ -120,6 +120,9 @@ type Mutation {
   # Split a log
   splitLog(input: LogSplitInput!): Log!
 
+  # Merge a log
+  mergeLog(input: LogMergeInput!): Log!
+
   # Edit a log
   editLog(input: LogEditInput!): Log!
 
diff --git a/graph2/schema/types/Log.gql b/graph2/schema/types/Log.gql
index c476d2a..563ad9e 100644
--- a/graph2/schema/types/Log.gql
+++ b/graph2/schema/types/Log.gql
@@ -129,10 +129,24 @@ input LogSplitInput {
   "Log ID"
   logId: String!
 
-  "After Post ID"
+  "Split out all posts from and including the post with this ID"
   startPostId: String!
 }
 
+"""
+Input for mergeLog mutation.
+"""
+input LogMergeInput {
+  "Target log ID"
+  targetLogId: String!
+
+  "Source log ID"
+  sourceLogId: String!
+
+  "Remove the source log after merging"
+  removeAfter: Boolean
+}
+
 enum LogImporter {
   """
   mIRC-like: This importer parses logs that copied from mIRC posts without spaces.
diff --git a/services/logs.go b/services/logs.go
index 2c3fbf9..485517f 100644
--- a/services/logs.go
+++ b/services/logs.go
@@ -280,12 +280,78 @@ func (s *LogService) SplitLog(ctx context.Context, logId string, startPostId str
 	s.changeService.Submit(ctx, models.ChangeModelPost, "add", true, changekeys.Many(newLog, newPosts), newPosts)
 
 	// Refresh character lists.
-	_ = s.refreshLogCharacters(ctx, *l, nil)
-	_ = s.refreshLogCharacters(ctx, *newLog, nil)
+	_, _ = s.refreshLogCharacters(ctx, *l, nil)
+	newLog2, err := s.refreshLogCharacters(ctx, *newLog, nil)
+	if err == nil {
+		newLog = newLog2
+	}
 
 	return newLog, nil
 }
 
+func (s *LogService) MergeLogs(ctx context.Context, targetID string, sourceID string, removeAfter bool) (*models.Log, error) {
+	// Check permissions
+	if err := auth.CheckPermission(ctx, "edit", &models.Log{}); err != nil {
+		return nil, err
+	}
+	if removeAfter {
+		if err := auth.CheckPermission(ctx, "remove", &models.Log{}); err != nil {
+			return nil, err
+		}
+	}
+
+	// Merge log posts into log.
+	source, err := s.logs.Find(ctx, sourceID)
+	if err != nil {
+		return nil, errors.New("could not find source log: " + err.Error())
+	}
+	target, err := s.logs.Find(ctx, targetID)
+	if err != nil {
+		return nil, errors.New("could not find target log: " + err.Error())
+	}
+
+	// Get the source posts.
+	posts, err := s.posts.List(ctx, models.PostFilter{LogID: &source.ShortID})
+	if err != nil {
+		return nil, errors.New("could not fetch source posts: " + err.Error())
+	}
+
+	// Associate the posts with the target logs
+	for _, post := range posts {
+		post.ID = ""
+		post.LogID = target.ShortID
+	}
+
+	// Insert them
+	posts, err = s.posts.InsertMany(ctx, posts...)
+	if err != nil {
+		return nil, errors.New("could not insert posts into target: " + err.Error())
+	}
+
+	// Remove other log
+	if removeAfter {
+		err = s.logs.Delete(ctx, *source)
+		if err != nil {
+			return nil, errors.New("posts have been inserted, but could not remove source: " + err.Error())
+		}
+
+		s.changeService.Submit(ctx, models.ChangeModelLog, "remove", true, changekeys.Listed(source), source)
+	}
+
+	// Refresh characters
+	target2, err := s.refreshLogCharacters(ctx, *target, nil)
+	if err != nil {
+		log.Printf("Failed to update characters in log %s: %s", target.ID, err)
+	} else {
+		target = target2
+	}
+
+	// Submit changes after the target
+	s.changeService.Submit(ctx, models.ChangeModelPost, "add", true, changekeys.Many(target, posts), target, posts)
+
+	return target, nil
+}
+
 func (s *LogService) AddPost(ctx context.Context, logId string, time time.Time, kind, nick, text string) (*models.Post, error) {
 	if kind == "" || nick == "" || time.IsZero() {
 		return nil, errors.New("kind, nick and time must be non-empty")
@@ -313,9 +379,11 @@ func (s *LogService) AddPost(ctx context.Context, logId string, time time.Time,
 		return nil, err
 	}
 
-	err = s.refreshLogCharacters(ctx, *l, nil)
+	l2, err := s.refreshLogCharacters(ctx, *l, nil)
 	if err != nil {
 		log.Printf("Failed to update characters in log %s: %s", l.ID, err)
+	} else {
+		l = l2
 	}
 
 	s.changeService.Submit(ctx, models.ChangeModelPost, "add", true, changekeys.Many(l, post), post)
@@ -348,7 +416,7 @@ func (s *LogService) EditPost(ctx context.Context, id string, update models.Post
 			return
 		}
 
-		err = s.refreshLogCharacters(ctx, *l, nil)
+		_, err = s.refreshLogCharacters(ctx, *l, nil)
 		if err != nil {
 			log.Printf("Failed to update characters in log %s: %s", l.ID, err)
 		}
@@ -415,7 +483,7 @@ func (s *LogService) DeletePost(ctx context.Context, id string) (*models.Post, e
 			return
 		}
 
-		err = s.refreshLogCharacters(ctx, *l, nil)
+		_, err = s.refreshLogCharacters(ctx, *l, nil)
 		if err != nil {
 			log.Printf("Failed to update characters in log %s: %s", l.ID, err)
 		}
@@ -575,7 +643,8 @@ func (s *LogService) RefreshAllLogCharacters(ctx context.Context) error {
 		l := logs[i]
 
 		eg.Go(func() error {
-			return s.refreshLogCharacters(ctx, *l, characterMap)
+			_, err := s.refreshLogCharacters(ctx, *l, characterMap)
+			return err
 		})
 	}
 	err = eg.Wait()
@@ -588,14 +657,14 @@ func (s *LogService) RefreshAllLogCharacters(ctx context.Context) error {
 	return nil
 }
 
-func (s *LogService) RefreshLogCharacters(ctx context.Context, log models.Log) error {
+func (s *LogService) RefreshLogCharacters(ctx context.Context, log models.Log) (*models.Log, error) {
 	return s.refreshLogCharacters(ctx, log, nil)
 }
 
-func (s *LogService) refreshLogCharacters(ctx context.Context, log models.Log, characterMap map[string]*models.Character) error {
+func (s *LogService) refreshLogCharacters(ctx context.Context, log models.Log, characterMap map[string]*models.Character) (*models.Log, error) {
 	posts, err := s.ListPosts(ctx, &models.PostFilter{LogID: &log.ShortID})
 	if err != nil {
-		return nil
+		return &log, nil
 	}
 
 	counts := make(map[string]int)
@@ -639,7 +708,7 @@ func (s *LogService) refreshLogCharacters(ctx context.Context, log models.Log, c
 	if characterMap == nil {
 		characters, err := s.characterService.List(ctx, models.CharacterFilter{Nicks: nicks})
 		if err != nil {
-			return err
+			return nil, err
 		}
 
 		characterMap = s.makeCharacterMap(characters)
@@ -659,8 +728,7 @@ func (s *LogService) refreshLogCharacters(ctx context.Context, log models.Log, c
 		log.CharacterIDs = append(log.CharacterIDs, character.ID)
 	}
 
-	_, err = s.logs.Update(ctx, log, models.LogUpdate{CharacterIDs: log.CharacterIDs})
-	return err
+	return s.logs.Update(ctx, log, models.LogUpdate{CharacterIDs: log.CharacterIDs})
 }
 
 func (s *LogService) makeCharacterMap(characters []*models.Character) map[string]*models.Character {