diff --git a/src/Firefly.cs b/src/Firefly.cs
index a1d2280..be3bbba 100644
--- a/src/Firefly.cs
+++ b/src/Firefly.cs
@@ -188,7 +188,10 @@ namespace Firefly
 
                     case "LINDEX":
                         return HandleLIndexCommand(parts.Length > 1 ? string.Join(" ", parts.Skip(1)) : "");
-                    
+
+                    case "LLEN":
+                        return HandleLLengthCommand(parts.Length > 1 ? parts[1] : "");
+
                     case "LRANGE":
                         return HandleLRangeCommand(parts.Length > 1 ? string.Join(" ", parts.Skip(1)) : "");
 
diff --git a/src/ListOperations.cs b/src/ListOperations.cs
index 716af73..58fb450 100644
--- a/src/ListOperations.cs
+++ b/src/ListOperations.cs
@@ -152,6 +152,30 @@ namespace Firefly
                 : Encoding.UTF8.GetBytes("$-1\r\n");
         }
 
+        /// <summary>
+        /// Handles the LLEN command which returns the length of a list.
+        /// </summary>
+        /// <param name="args">Command arguments containing the key</param>
+        /// <returns>The length of the list or 0 if the key does not exist</returns>
+        static byte[] HandleLLengthCommand(string args)
+        {
+            if (string.IsNullOrWhiteSpace(args))
+            {
+                return Encoding.UTF8.GetBytes("-ERR wrong number of arguments for 'llen' command\r\n");
+            }
+
+            string key = args.Trim();
+            int length = 0;
+
+            // Use helper function to safely read the list with read lock
+            ListStoreWithReadLock(key, list =>
+            {
+                length = list.Count;
+            });
+
+            return Encoding.UTF8.GetBytes($":{length}\r\n");
+        }
+
         /// <summary>
         /// Handles the LRANGE command which returns a range of elements from a list.
         /// </summary>