EnvDTE.DTE dte = (EnvDTE.DTE)System.Runtime.InteropServices.Marshal.GetActiveObject("VisualStudio.DTE"); string solutionDir = System.IO.Path.GetDirectoryName(dte.Solution.FullName);

But, this returns the solution directory for the add ins, not the current solution.

Your approach to get the directory is good. What s wrong is the way you get the VisualStudio.DTE object. Where is this code called? I assume it is in your add-in. Do you execute (debug) your add-in in Visual Studio which opens another instance of Visual Studio where you open your solution? So you have two instances of Visual Studio.

The GetActiveObject("VisualStudio.DTE") gets a random Visual Studio instance. In your case, it is apparently Visual Studio with an add-in project since you get path to your add-in. That s for explanation what would be the reason of your problem.

The correct way to get DTE is very simple. In fact, your add-in already has reference to DTE in which it runs (that is, in which the solution is opened). It is stored in a global variable _applicationObject in your add-in connect class. It is set when your add-in starts in the OnConnection event handler. So all you need is to call:

string solutionDir = System.IO.Path.GetDirectoryName(_applicationObject.Solution.FullName);

With Peter s push in the right direction, I set up the context menu addin to launch an external tool with the solution directory, and output the results to the output pane. Some example blurb from the add in:

    ///--------------------------------------------------------------------------------
    /// <summary>This method implements the OnConnection method of the IDTExtensibility2 interface. Receives notification that the Add-in is being loaded.</summary>
    ///
    /// <param term= application >Root object of the host application.</param>
    /// <param term= connectMode >Describes how the Add-in is being loaded.</param>
    /// <param term= addInInst >Object representing this Add-in.</param>
    /// <seealso class= IDTExtensibility2  />
    ///--------------------------------------------------------------------------------
    public void OnConnection(object application, ext_ConnectMode connectMode, object addInInst, ref Array custom)
    {
        _applicationObject = (DTE2)application;
        _addInInstance = (AddIn)addInInst;

        // Get the solution command bar
        CommandBar solutionCommandBar = ((CommandBars)_applicationObject.CommandBars)["Solution"];

        // Set up the main InCode
        CommandBarPopup solutionPopup = (CommandBarPopup)solutionCommandBar.Controls.Add(MsoControlType.msoControlPopup, System.Reflection.Missing.Value, System.Reflection.Missing.Value, 1, true);
        solutionPopup.Caption = "InCode";

        // Add solution updater submenu
        CommandBarControl solutionUpdaterControl = solutionPopup.Controls.Add(MsoControlType.msoControlButton, System.Reflection.Missing.Value, System.Reflection.Missing.Value, 1, true);
        solutionUpdaterControl.Caption = "Update Solution";
        updateSolutionMenuItemHandler = (CommandBarEvents)_applicationObject.Events.get_CommandBarEvents(solutionUpdaterControl);
        updateSolutionMenuItemHandler.Click += new _dispCommandBarControlEvents_ClickEventHandler(updateSolution_Click);
    }

    // The event handlers for the solution submenu items
    CommandBarEvents updateSolutionMenuItemHandler;

    ///--------------------------------------------------------------------------------
    /// <summary>This property gets the solution updater output pane.</summary>
    ///--------------------------------------------------------------------------------
    protected OutputWindowPane _solutionUpdaterPane = null;
    protected OutputWindowPane SolutionUpdaterPane
    {
        get
        {
            if (_solutionUpdaterPane == null)
            {
                OutputWindow outputWindow = _applicationObject.ToolWindows.OutputWindow;
                foreach (OutputWindowPane loopPane in outputWindow.OutputWindowPanes)
                {
                    if (loopPane.Name == "Solution Updater")
                    {
                        _solutionUpdaterPane = loopPane;
                        return _solutionUpdaterPane;
                    }
                }
                _solutionUpdaterPane = outputWindow.OutputWindowPanes.Add("Solution Updater");
            }
            return _solutionUpdaterPane;
        }
    }

    ///--------------------------------------------------------------------------------
    /// <summary>This method handles clicking on the Update Solution submenu.</summary>
    ///
    /// <param term= inputCommandBarControl >The control that is source of the click.</param>
    /// <param term= handled >Handled flag.</param>
    /// <param term= cancelDefault >Cancel default flag.</param>
    ///--------------------------------------------------------------------------------
    protected void updateSolution_Click(object inputCommandBarControl, ref bool handled, ref bool cancelDefault)
    {
        try
        {
            // set up and execute solution updater thread
            UpdateSolutionDelegate updateSolutionDelegate = UpdateSolution;
            updateSolutionDelegate.BeginInvoke(UpdateSolutionCompleted, updateSolutionDelegate);
        }
        catch (System.Exception ex)
        {
            // put exception message in output pane
            SolutionUpdaterPane.OutputString(ex.Message);
        }
    }

    protected delegate void UpdateSolutionDelegate();

    ///--------------------------------------------------------------------------------
    /// <summary>This method launches the solution updater to update the solution.</summary>
    ///--------------------------------------------------------------------------------
    protected void UpdateSolution()
    {
        try
        {
            // set up solution updater process
            string solutionDir = System.IO.Path.GetDirectoryName(_applicationObject.Solution.FullName);
            System.Diagnostics.ProcessStartInfo procStartInfo = new System.Diagnostics.ProcessStartInfo(@"SolutionUpdater.exe", solutionDir);
            procStartInfo.RedirectStandardOutput = true;
            procStartInfo.UseShellExecute = false;
            procStartInfo.CreateNoWindow = true;
            System.Diagnostics.Process proc = new System.Diagnostics.Process();
            proc.StartInfo = procStartInfo;

            // execute the solution updater
            proc.Start();

            // put solution updater output to output pane
            SolutionUpdaterPane.OutputString(proc.StandardOutput.ReadToEnd());
            SolutionUpdaterPane.OutputString("Solution update complete.");
        }
        catch (System.Exception ex)
        {
            // put exception message in output pane
            SolutionUpdaterPane.OutputString(ex.Message);
        }
    }

    ///--------------------------------------------------------------------------------
    /// <summary>This method completing the update solution thread.</summary>
    ///
    /// <param name="ar">IAsyncResult.</param>
    ///--------------------------------------------------------------------------------
    protected void UpdateSolutionCompleted(IAsyncResult ar)
    {
        try
        {
            if (ar == null) throw new ArgumentNullException("ar");

            UpdateSolutionDelegate updateSolutionDelegate = ar.AsyncState as UpdateSolutionDelegate;
            Trace.Assert(updateSolutionDelegate != null, "Invalid object type");

            updateSolutionDelegate.EndInvoke(ar);
        }
        catch (System.Exception ex)
        {
            // put exception message in output pane
            SolutionUpdaterPane.OutputString(ex.Message);
        }
    }