diff --git a/src/LibHac/Fs/ProgramIndexMapInfo.cs b/src/LibHac/Fs/ProgramIndexMapInfo.cs
new file mode 100644
index 00000000..7e221870
--- /dev/null
+++ b/src/LibHac/Fs/ProgramIndexMapInfo.cs
@@ -0,0 +1,13 @@
+using System.Runtime.InteropServices;
+using LibHac.Ncm;
+
+namespace LibHac.Fs
+{
+    [StructLayout(LayoutKind.Explicit, Size = 0x20)]
+    public struct ProgramIndexMapInfo
+    {
+        [FieldOffset(0x00)] public ProgramId ProgramId;
+        [FieldOffset(0x08)] public ProgramId MainProgramId;
+        [FieldOffset(0x10)] public byte ProgramIndex;
+    }
+}
diff --git a/src/LibHac/FsSrv/ProgramIndexMapInfoManager.cs b/src/LibHac/FsSrv/ProgramIndexMapInfoManager.cs
new file mode 100644
index 00000000..2adb6a76
--- /dev/null
+++ b/src/LibHac/FsSrv/ProgramIndexMapInfoManager.cs
@@ -0,0 +1,103 @@
+using System;
+using System.Collections.Generic;
+using LibHac.Fs;
+using LibHac.Ncm;
+
+namespace LibHac.FsSrv
+{
+    public class ProgramIndexMapInfoManager
+    {
+        private LinkedList<ProgramIndexMapInfo> MapEntries { get; } = new LinkedList<ProgramIndexMapInfo>();
+
+        /// <summary>
+        /// Clears any existing 
+        /// </summary>
+        /// <param name="entries">The entries </param>
+        /// <returns><see cref="Result.Success"/>: The operation was successful.</returns>
+        public Result Reset(ReadOnlySpan<ProgramIndexMapInfo> entries)
+        {
+            lock (MapEntries)
+            {
+                ClearImpl();
+
+                for (int i = 0; i < entries.Length; i++)
+                {
+                    MapEntries.AddLast(entries[i]);
+                }
+
+                return Result.Success;
+            }
+        }
+
+        public void Clear()
+        {
+            lock (MapEntries)
+            {
+                ClearImpl();
+            }
+        }
+
+        public ProgramIndexMapInfo? Get(ProgramId programId)
+        {
+            lock (MapEntries)
+            {
+                return GetImpl((in ProgramIndexMapInfo x) => x.ProgramId == programId);
+            }
+        }
+
+        /// <summary>
+        /// Gets the <see cref="ProgramId"/> of the program with index <paramref name="programIndex"/> in the
+        /// multi-program app <paramref name="programId"/> is part of.
+        /// </summary>
+        /// <param name="programId">A program ID in the multi-program app to query.</param>
+        /// <param name="programIndex">The index of the program to get.</param>
+        /// <returns>If the program exists, the ID of the program with the specified index,
+        /// otherwise <see cref="ProgramId.InvalidId"/></returns>
+        public ProgramId GetProgramId(ProgramId programId, byte programIndex)
+        {
+            lock (MapEntries)
+            {
+                ProgramIndexMapInfo? mainProgramMapInfo = GetImpl((in ProgramIndexMapInfo x) => x.ProgramId == programId);
+
+                if(!mainProgramMapInfo.HasValue)
+                    return ProgramId.InvalidId;
+
+                ProgramIndexMapInfo? requestedMapInfo = GetImpl((in ProgramIndexMapInfo x) =>
+                    x.MainProgramId == mainProgramMapInfo.Value.MainProgramId && x.ProgramIndex == programIndex);
+
+                if (!requestedMapInfo.HasValue)
+                    return ProgramId.InvalidId;
+
+                return requestedMapInfo.Value.ProgramId;
+            }
+        }
+
+        public int GetProgramCount()
+        {
+            lock (MapEntries)
+            {
+                return MapEntries.Count;
+            }
+        }
+
+        private delegate bool EntrySelector(in ProgramIndexMapInfo candidate);
+
+        private ProgramIndexMapInfo? GetImpl(EntrySelector selector)
+        {
+            foreach (ProgramIndexMapInfo entry in MapEntries)
+            {
+                if (selector(in entry))
+                {
+                    return entry;
+                }
+            }
+
+            return null;
+        }
+
+        private void ClearImpl()
+        {
+            MapEntries.Clear();
+        }
+    }
+}
diff --git a/src/LibHac/FsSrv/ProgramRegistryServiceImpl.cs b/src/LibHac/FsSrv/ProgramRegistryServiceImpl.cs
index e57fb497..90f5cfb2 100644
--- a/src/LibHac/FsSrv/ProgramRegistryServiceImpl.cs
+++ b/src/LibHac/FsSrv/ProgramRegistryServiceImpl.cs
@@ -8,10 +8,12 @@ namespace LibHac.FsSrv
     public class ProgramRegistryServiceImpl
     {
         private ProgramRegistryManager RegistryManager { get; }
+        private ProgramIndexMapInfoManager ProgramIndexManager { get; }
 
         public ProgramRegistryServiceImpl(FileSystemServer fsServer)
         {
             RegistryManager = new ProgramRegistryManager(fsServer);
+            ProgramIndexManager = new ProgramIndexMapInfoManager();
         }
 
         /// <summary>
@@ -67,5 +69,18 @@ namespace LibHac.FsSrv
         {
             return RegistryManager.GetProgramInfoByProgramId(out programInfo, programId);
         }
+
+        /// <summary>
+        /// Gets the <see cref="ProgramId"/> of the program with index <paramref name="programIndex"/> in the
+        /// multi-program app <paramref name="programId"/> is part of.
+        /// </summary>
+        /// <param name="programId">A program ID in the multi-program app to query.</param>
+        /// <param name="programIndex">The index of the program to get.</param>
+        /// <returns>If the program exists, the ID of the program with the specified index,
+        /// otherwise <see cref="ProgramId.InvalidId"/></returns>
+        public ProgramId GetProgramId(ProgramId programId, byte programIndex)
+        {
+            return ProgramIndexManager.GetProgramId(programId, programIndex);
+        }
     }
 }