diff --git a/src/NTwain/DSM/OSXLegacyDSM.cs b/src/NTwain/DSM/OSXLegacyDSM.cs
index 06dc69f..de65b24 100644
--- a/src/NTwain/DSM/OSXLegacyDSM.cs
+++ b/src/NTwain/DSM/OSXLegacyDSM.cs
@@ -93,5 +93,26 @@ namespace NTwain.DSM
         MSG msg,
         ref TW_CUSTOMDSDATA twcustomedsdata
     );
+
+    [DllImport(DsmName, CharSet = CharSet.Ansi)]
+    internal static extern UInt16 DSM_Entry
+    (
+        ref TW_IDENTITY_MACOSX origin,
+        ref TW_IDENTITY_MACOSX dest,
+        DG dg,
+        DAT dat,
+        MSG msg,
+        ref TW_CALLBACK twcallback
+    );
+    [DllImport(DsmName, CharSet = CharSet.Ansi)]
+    internal static extern UInt16 DSM_Entry
+    (
+        ref TW_IDENTITY_MACOSX origin,
+        ref TW_IDENTITY_MACOSX dest,
+        DG dg,
+        DAT dat,
+        MSG msg,
+        ref TW_CALLBACK2 twcallback
+    );
   }
 }
diff --git a/src/NTwain/DSM/OSXNewDSM.cs b/src/NTwain/DSM/OSXNewDSM.cs
index 9ef0f42..05b159c 100644
--- a/src/NTwain/DSM/OSXNewDSM.cs
+++ b/src/NTwain/DSM/OSXNewDSM.cs
@@ -93,5 +93,26 @@ namespace NTwain.DSM
         MSG msg,
         ref TW_CUSTOMDSDATA twcustomedsdata
     );
+
+    [DllImport(DsmName, CharSet = CharSet.Ansi)]
+    internal static extern UInt16 DSM_Entry
+    (
+        ref TW_IDENTITY_MACOSX origin,
+        ref TW_IDENTITY_MACOSX dest,
+        DG dg,
+        DAT dat,
+        MSG msg,
+        ref TW_CALLBACK twcallback
+    );
+    [DllImport(DsmName, CharSet = CharSet.Ansi)]
+    internal static extern UInt16 DSM_Entry
+    (
+        ref TW_IDENTITY_MACOSX origin,
+        ref TW_IDENTITY_MACOSX dest,
+        DG dg,
+        DAT dat,
+        MSG msg,
+        ref TW_CALLBACK2 twcallback
+    );
   }
 }
diff --git a/src/NTwain/DSM/WinLegacyDSM.cs b/src/NTwain/DSM/WinLegacyDSM.cs
index d4d76d3..6b19c09 100644
--- a/src/NTwain/DSM/WinLegacyDSM.cs
+++ b/src/NTwain/DSM/WinLegacyDSM.cs
@@ -93,5 +93,26 @@ namespace NTwain.DSM
         MSG msg,
         ref TW_CUSTOMDSDATA twcustomedsdata
     );
+
+    [DllImport(DsmName, CharSet = CharSet.Ansi)]
+    internal static extern UInt16 DSM_Entry
+    (
+        ref TW_IDENTITY_LEGACY origin,
+        ref TW_IDENTITY_LEGACY dest,
+        DG dg,
+        DAT dat,
+        MSG msg,
+        ref TW_CALLBACK twcallback
+    );
+    [DllImport(DsmName, CharSet = CharSet.Ansi)]
+    internal static extern UInt16 DSM_Entry
+    (
+        ref TW_IDENTITY_LEGACY origin,
+        ref TW_IDENTITY_LEGACY dest,
+        DG dg,
+        DAT dat,
+        MSG msg,
+        ref TW_CALLBACK2 twcallback
+    );
   }
 }
diff --git a/src/NTwain/DSM/WinNewDSM.cs b/src/NTwain/DSM/WinNewDSM.cs
index c2d693c..4eb42b5 100644
--- a/src/NTwain/DSM/WinNewDSM.cs
+++ b/src/NTwain/DSM/WinNewDSM.cs
@@ -93,5 +93,26 @@ namespace NTwain.DSM
         MSG msg,
         ref TW_CUSTOMDSDATA twcustomedsdata
     );
+
+    [DllImport(DsmName, CharSet = CharSet.Ansi)]
+    internal static extern UInt16 DSM_Entry
+    (
+        ref TW_IDENTITY_LEGACY origin,
+        ref TW_IDENTITY_LEGACY dest,
+        DG dg,
+        DAT dat,
+        MSG msg,
+        ref TW_CALLBACK twcallback
+    );
+    [DllImport(DsmName, CharSet = CharSet.Ansi)]
+    internal static extern UInt16 DSM_Entry
+    (
+        ref TW_IDENTITY_LEGACY origin,
+        ref TW_IDENTITY_LEGACY dest,
+        DG dg,
+        DAT dat,
+        MSG msg,
+        ref TW_CALLBACK2 twcallback
+    );
   }
 }
diff --git a/src/NTwain/Triplets/DATCallback.cs b/src/NTwain/Triplets/DATCallback.cs
new file mode 100644
index 0000000..5f2d2aa
--- /dev/null
+++ b/src/NTwain/Triplets/DATCallback.cs
@@ -0,0 +1,57 @@
+using NTwain.DSM;
+using TWAINWorkingGroup;
+
+namespace NTwain.Triplets
+{
+  /// <summary>
+  /// Contains calls used with <see cref="DG.CONTROL"/> and <see cref="DAT.CALLBACK"/>.
+  /// </summary>
+  public class DATCallback : TripletBase
+  {
+    public DATCallback(TwainSession session) : base(session)
+    {
+    }
+
+    /// <summary>
+    /// Registers the callback function.
+    /// </summary>
+    /// <param name="data"></param>
+    /// <returns></returns>
+    public STS RegisterCallback(ref TW_CALLBACK data)
+    {
+      return DoIt(MSG.REGISTER_CALLBACK, ref data);
+    }
+
+    STS DoIt(MSG msg, ref TW_CALLBACK data)
+    {
+      var rc = STS.FAILURE;
+      if (TwainPlatform.IsWindows)
+      {
+        var app = Session.AppIdentity;
+        var ds = Session.CurrentSource;
+        if (TwainPlatform.Is32bit && TwainPlatform.PreferLegacyDSM)
+        {
+          rc = (STS)WinLegacyDSM.DSM_Entry(ref app, ref ds, DG.CONTROL, DAT.DEVICEEVENT, msg, ref data);
+        }
+        else
+        {
+          rc = (STS)WinNewDSM.DSM_Entry(ref app, ref ds, DG.CONTROL, DAT.DEVICEEVENT, msg, ref data);
+        }
+      }
+      else if (TwainPlatform.IsMacOSX)
+      {
+        TW_IDENTITY_MACOSX app = Session.AppIdentity;
+        TW_IDENTITY_MACOSX ds = Session.CurrentSource;
+        if (TwainPlatform.PreferLegacyDSM)
+        {
+          rc = (STS)OSXLegacyDSM.DSM_Entry(ref app, ref ds, DG.CONTROL, DAT.DEVICEEVENT, msg, ref data);
+        }
+        else
+        {
+          rc = (STS)OSXNewDSM.DSM_Entry(ref app, ref ds, DG.CONTROL, DAT.DEVICEEVENT, msg, ref data);
+        }
+      }
+      return rc;
+    }
+  }
+}
diff --git a/src/NTwain/Triplets/DATCallback2.cs b/src/NTwain/Triplets/DATCallback2.cs
new file mode 100644
index 0000000..130cf3f
--- /dev/null
+++ b/src/NTwain/Triplets/DATCallback2.cs
@@ -0,0 +1,57 @@
+using NTwain.DSM;
+using TWAINWorkingGroup;
+
+namespace NTwain.Triplets
+{
+  /// <summary>
+  /// Contains calls used with <see cref="DG.CONTROL"/> and <see cref="DAT.CALLBACK2"/>.
+  /// </summary>
+  public class DATCallback2 : TripletBase
+  {
+    public DATCallback2(TwainSession session) : base(session)
+    {
+    }
+
+    /// <summary>
+    /// Registers the callback function.
+    /// </summary>
+    /// <param name="data"></param>
+    /// <returns></returns>
+    public STS RegisterCallback(ref TW_CALLBACK2 data)
+    {
+      return DoIt(MSG.REGISTER_CALLBACK, ref data);
+    }
+
+    STS DoIt(MSG msg, ref TW_CALLBACK2 data)
+    {
+      var rc = STS.FAILURE;
+      if (TwainPlatform.IsWindows)
+      {
+        var app = Session.AppIdentity;
+        var ds = Session.CurrentSource;
+        if (TwainPlatform.Is32bit && TwainPlatform.PreferLegacyDSM)
+        {
+          rc = (STS)WinLegacyDSM.DSM_Entry(ref app, ref ds, DG.CONTROL, DAT.DEVICEEVENT, msg, ref data);
+        }
+        else
+        {
+          rc = (STS)WinNewDSM.DSM_Entry(ref app, ref ds, DG.CONTROL, DAT.DEVICEEVENT, msg, ref data);
+        }
+      }
+      else if (TwainPlatform.IsMacOSX)
+      {
+        TW_IDENTITY_MACOSX app = Session.AppIdentity;
+        TW_IDENTITY_MACOSX ds = Session.CurrentSource;
+        if (TwainPlatform.PreferLegacyDSM)
+        {
+          rc = (STS)OSXLegacyDSM.DSM_Entry(ref app, ref ds, DG.CONTROL, DAT.DEVICEEVENT, msg, ref data);
+        }
+        else
+        {
+          rc = (STS)OSXNewDSM.DSM_Entry(ref app, ref ds, DG.CONTROL, DAT.DEVICEEVENT, msg, ref data);
+        }
+      }
+      return rc;
+    }
+  }
+}
diff --git a/src/NTwain/Triplets/DATIdentity.cs b/src/NTwain/Triplets/DATIdentity.cs
index 0f6057a..421fc7f 100644
--- a/src/NTwain/Triplets/DATIdentity.cs
+++ b/src/NTwain/Triplets/DATIdentity.cs
@@ -24,16 +24,8 @@ namespace NTwain.Triplets
       if ((rc = DoIt(MSG.OPENDS, ref ds)) == STS.SUCCESS)
       {
         Session.CurrentSource = ds;
+        Session.RegisterCallback();
         Session.State = STATE.S4;
-        //// determine memory mgmt routines used
-        //if ((((DG)Session._appIdentity.SupportedGroups) & DG.DSM2) == DG.DSM2)
-        //{
-        //  TW_ENTRYPOINT_DELEGATES entry = default;
-        //  if (Session.DGControl.EntryPoint.Get(ref entry) == STS.SUCCESS)
-        //  {
-        //    Session._entryPoint = entry;
-        //  }
-        //}
       }
       return rc;
     }
@@ -48,8 +40,8 @@ namespace NTwain.Triplets
       var ds = Session.CurrentSource;
       if ((rc = DoIt(MSG.CLOSEDS, ref ds)) == STS.SUCCESS)
       {
-        Session.CurrentSource = default;
         Session.State = STATE.S3;
+        Session.CurrentSource = default;
       }
       return rc;
     }
diff --git a/src/NTwain/Triplets/DATParent.cs b/src/NTwain/Triplets/DATParent.cs
index 79ba354..ce810fa 100644
--- a/src/NTwain/Triplets/DATParent.cs
+++ b/src/NTwain/Triplets/DATParent.cs
@@ -24,7 +24,6 @@ namespace NTwain.Triplets
       if ((rc = DoIt(MSG.OPENDSM, ref hwnd)) == STS.SUCCESS)
       {
         Session._hwnd = hwnd;
-        Session.State = STATE.S3;
 
         // get default source
         if (Session.DGControl.Identity.GetDefault(out TW_IDENTITY_LEGACY ds) == STS.SUCCESS)
@@ -40,6 +39,7 @@ namespace NTwain.Triplets
             Session._entryPoint = entry;
           }
         }
+        Session.State = STATE.S3;
       }
       return rc;
     }
@@ -54,9 +54,10 @@ namespace NTwain.Triplets
       STS rc;
       if ((rc = DoIt(MSG.CLOSEDSM, ref hwnd)) == STS.SUCCESS)
       {
-        Session._hwnd = IntPtr.Zero;
-        Session._entryPoint = default;
         Session.State = STATE.S2;
+        Session._entryPoint = default;
+        Session.DefaultSource = default;
+        Session._hwnd = IntPtr.Zero;
       }
       return rc;
     }
diff --git a/src/NTwain/Triplets/DGControl.cs b/src/NTwain/Triplets/DGControl.cs
index 4622ce1..18ec0bc 100644
--- a/src/NTwain/Triplets/DGControl.cs
+++ b/src/NTwain/Triplets/DGControl.cs
@@ -30,5 +30,11 @@
     private DATDeviceEvent? _deviceEvent;
     public DATDeviceEvent DeviceEvent => _deviceEvent ??= new DATDeviceEvent(Session);
 
+    private DATCallback? _callback;
+    public DATCallback Callback => _callback ??= new DATCallback(Session);
+
+    private DATCallback2? _callback2;
+    public DATCallback2 Callback2 => _callback2 ??= new DATCallback2(Session);
+
   }
 }
\ No newline at end of file
diff --git a/src/NTwain/TwainSession.Callbacks.cs b/src/NTwain/TwainSession.Callbacks.cs
new file mode 100644
index 0000000..e3c16ef
--- /dev/null
+++ b/src/NTwain/TwainSession.Callbacks.cs
@@ -0,0 +1,91 @@
+using System;
+using System.Runtime.InteropServices;
+using TWAINWorkingGroup;
+
+namespace NTwain
+{
+  // this file contains callback methods
+
+  partial class TwainSession
+  {
+    // these are kept around while a callback ptr is registered so they
+    // don't get gc'd
+    readonly NativeMethods.WindowsDsmEntryCallbackDelegate _legacyCallbackDelegate;
+    readonly NativeMethods.MacosxDsmEntryCallbackDelegate _osxCallbackDelegate;
+
+    /// <summary>
+    /// Try to registers callbacks for after opening the source.
+    /// </summary>
+    internal void RegisterCallback()
+    {
+      IntPtr cbPtr = IntPtr.Zero;
+
+      if (TwainPlatform.IsMacOSX)
+      {
+        cbPtr = Marshal.GetFunctionPointerForDelegate(_osxCallbackDelegate);
+      }
+      else
+      {
+        cbPtr = Marshal.GetFunctionPointerForDelegate(_legacyCallbackDelegate);
+      }
+
+      var rc = STS.FAILURE;
+
+      // per the spec (pg 8-10), apps for 2.2 or higher uses callback2 so try this first
+      if (_appIdentity.ProtocolMajor > 2 || (_appIdentity.ProtocolMajor >= 2 && _appIdentity.ProtocolMinor >= 2))
+      {
+        var cb2 = new TW_CALLBACK2 { CallBackProc = cbPtr };
+        rc = DGControl.Callback2.RegisterCallback(ref cb2);
+      }
+      if (rc != STS.SUCCESS)
+      {
+        // always try old callback
+        var cb = new TW_CALLBACK { CallBackProc = cbPtr };
+        DGControl.Callback.RegisterCallback(ref cb);
+      }
+    }
+
+    private ushort LegacyCallbackHandler
+    (
+        ref TW_IDENTITY_LEGACY origin,
+        ref TW_IDENTITY_LEGACY dest,
+        DG dg,
+        DAT dat,
+        MSG msg,
+        IntPtr twnull
+    )
+    {
+      HandleSourceMsg(msg);
+      return (ushort)STS.SUCCESS;
+    }
+
+    private ushort OSXCallbackHandler
+    (
+        ref TW_IDENTITY_MACOSX origin,
+        ref TW_IDENTITY_MACOSX dest,
+        DG dg,
+        DAT dat,
+        MSG msg,
+        IntPtr twnull
+    )
+    {
+      HandleSourceMsg(msg);
+      return (ushort)STS.SUCCESS;
+    }
+
+    private void HandleSourceMsg(MSG msg)
+    {
+      switch (msg)
+      {
+        case MSG.XFERREADY:
+          break;
+        case MSG.DEVICEEVENT:
+          break;
+        case MSG.CLOSEDSOK:
+          break;
+        case MSG.CLOSEDSREQ:
+          break;
+      }
+    }
+  }
+}
diff --git a/src/NTwain/TwainSession.PropEvents.cs b/src/NTwain/TwainSession.PropEvents.cs
index c4bfe74..f83b3a9 100644
--- a/src/NTwain/TwainSession.PropEvents.cs
+++ b/src/NTwain/TwainSession.PropEvents.cs
@@ -2,6 +2,7 @@
 using System;
 using System.Runtime.InteropServices;
 using TWAINWorkingGroup;
+using static System.Collections.Specialized.BitVector32;
 
 namespace NTwain
 {
@@ -151,6 +152,5 @@ namespace NTwain
     /// Fires when <see cref="CurrentSource"/> changes.
     /// </summary>
     public event Action<TwainSession, TW_IDENTITY_LEGACY>? CurrentSourceChanged;
-
   }
 }
diff --git a/src/NTwain/TwainSession.cs b/src/NTwain/TwainSession.cs
index 04935a0..c2f37f2 100644
--- a/src/NTwain/TwainSession.cs
+++ b/src/NTwain/TwainSession.cs
@@ -81,6 +81,9 @@ namespace NTwain
       DGControl = new DGControl(this);
       DGImage = new DGImage(this);
       DGAudio = new DGAudio(this);
+
+      _legacyCallbackDelegate = LegacyCallbackHandler;
+      _osxCallbackDelegate = OSXCallbackHandler;
     }
 
     internal IntPtr _hwnd;