The Telephony Application Programming Interface (TAPI) is an API, which enables PCs running Microsoft Windows to use telephone services. Different versions of TAPI are available on different versions of Windows. TAPI was introduced in 1993 as the result of joint development by Microsoft and Intel. The first publicly available version of TAPI was version 1.3, which was released as a patch on top of Microsoft Windows 3.1. Version 1.3 is no longer supported, although some MSDN development library CDs still contain the files and patch.

With Microsoft Windows 95, TAPI was integrated into the operating system. The first version on Windows 95 was TAPI 1.4. That version was not very different from 1.3. The biggest enhancement of TAPI 1.4 was support for 32-bit applications.

The TAPI standard supports both connections from individual computers and LAN connections serving any number of computers.

TAPI 2.0 was introduced with Windows NT 4.0. Version 2.0 was the first version on the Windows NT platform. It made a nice step forward by supporting some ACD and PBX specific functionality.

In 1997, Microsoft released TAPI version 2.1. This version of TAPI was available as a downloadable update and was the first version to be supported on both the Microsoft Windows 95 and NT/2000 platforms.

TAPI 3.0 was released in 1999 together with Windows 2000. This version enables IP telephony by providing simple and generic methods for making connections between two or more computers and now also offers the ability to access any media streams involved in the connection.

The Telephony Server Application Programming Interface (TSAPI) is a similar standard developed by Novell for NetWare servers.