Visual Studio Tools for Office (VSTO) is a set of development tools available in the form of a Visual Studio add-in (project templates) and a runtime that allows Microsoft Office 2003 and later versions of Office applications to host the .NET Framework Common Language Runtime (CLR) to expose their functionality via .NET. This allows extensions to the Office applications to be written in CLI compliant languages as well as to use functionality and user interface constructs from Office applications in .NET applications. Extensions to Office prior to Office 2003 only allowed the creation of COM add-ins using Visual Basic or Visual C++ and a "Developer" edition was also offered that enabled VBA developers to create COM Add-ins. VSTO supersedes developer editions of Office 2000 and Office XP for Office development. The developer editions of Office have been discontinued after Office XP and VSTO is available for Office 2003 and later versions only. The VSTO runtime, although part of VSTO development tools, is also downloadable separately if required. COM addin development is still possible for Office 2000 and all later versions using the Shared Add-in template in any version of Microsoft Visual Studio. The VSTO add-ins (project types and controls) are also developed using Visual Studio. For Visual Studio .NET 2003 and Visual Studio 2005, it was available only as a standalone edition with support for .NET languages limited to Visual Basic.NET and C#. It was also included as a part of the Visual Studio Team System 2005. Later on, the Visual Studio Tools for Office 2005 Second Edition (VSTO 2005 SE) was released as a free add-in to Visual Studio Professional and above that includes Office 2007 and 2003 support. However, for Visual Studio Professional Edition, it installs only the application-level add-ins; it does not add the document-level customizations or other functionality (actions pane, host controls, visual document designer, etc.) available in the full version of VSTO or Team System editions. The current version is Visual Studio Tools for Office 2012 (VSTO 4.5) which is compatible with Office 2016, Office 2013, Office 2010, and Office 2007. Comparison with VBA Like VBA, code written for VSTO is executed by a separate virtual machine (the CLR) which is hosted inside the Microsoft Office applications. However, unlike VBA, where the code is stored in the document file itself, programs written with VSTO are stored in separate CLI assemblies which are associated with the