Microsoft Visual Studio 2010, or Microsoft Visual Studio 2010 Express Edition. Alternatively, you can use the built-in Visual Studio Tools for Applications (VSTA) development environment in Revit. You must install VSTA from the Revit DVD separately from the Revit product installation. Microsoft has not yet announced when Visual Studio Tools for Applications (VSTA) for .NET 4.0 will be available. VSTA is the technology used for Revit macros. In the interim, run PrepareRevitForVSTA.bat before starting Revit to debug Revit macros. This script can be found in the Revit Program folder. Because this script will disable .NET 4.0 addins, run RestoreRevitFromVSTA.bat to restore Revit's default .NET 4.0 setting. For more information on writing applications using VSTA, see the section "Creating Macros with Revit VSTA" in the Revit 2012 User's Guide.