VBA Code

Installing and Uninstalling

The Add-ins collection contains all the add-ins that are available (and not just those that are installed).
You can refer to them explicitly using their name or by using a numerical index.

Addins("Analysis-ToolPak").Installed = True | False 
Addins("Analysis-ToolPak - VBA").Installed = False  'this does not work !!  
Addins(1).Installed = True | False 

List of Add-ins installed

This lists all the Excel add-ins that are installed and the folders they are saved in.

Public Sub Addins_List() 
Dim oAddin As AddIn 
Dim oCOMAddin As COMAddIn 
Dim icount As Integer 
Dim istart As Integer 
   For icount = 1 To Application.Addins.Count 
      Range("A" & icount).Value = Application.AddIns(icount).Name 
      Range("B" & icount).Value = Application.AddIns(icount).FullName 
      Range("C" & icount).Value = Application.AddIns(icount).Installed 
   Next icount 
   istart = icount 
   For icount = 1 To Application.COMAddIns.Count 
      Set oCOMAddIn = Application.COMAddIns(icount) 
      Range("A" & istart + icount).Value = Application.COMAddIns(icount).Description 
      Range("B" & istart + icount).Value = Application.COMAddIns(icount).progID 
      Range("C" & istart + icount).Value = Application.COMAddIns(icount).Connect 
   Next icount 
End Sub 

objaddin.CLSID - read only returns a unique identifier for the add-in 
objaddin.FullName - read only returns the full path and filename of the add-in 
objaddin.Installed - get/set whether the add-in is installed in the current session 
objaddin.Name - read only returns the filename of the add-in 
objaddin.Path - read only returns the full folder path of the add-in 
objaddin.Title - read only returns the string shown in the Add-in Manager (This is a hidden property) 

Application.LibraryPath

Returns the directory containing the built-in Excel add-ins.
Options > VBA Code > Folder Paths

Application.UserLibraryPath

Returns the directory to the location on the users computer where the COM add-ins are installed. Read Only string
Options > VBA Code > Folder Paths

Important

Do not use the "Auto_Open" event as it is only available for backwards compatibility.