(Microsoft Commercial Internet System) A family of Web server software products from Microsoft that runs on Windows NT and works with Internet Information Server (IIS). Intended for ISPs and other online services, it includes Web, chat, news and search servers and a variety of development tools. It also includes support for NetMeeting and provides an Internet-based messaging system that is different than Microsoft Exchange. MCIS was originally code named Normandy.

With the release of Microsoft's Exchange 2000 platform as the centerpiece of the company's hosted messaging technology, MCIS support was withdrawn in early 2003 with the recommendation to migrate to the .NET solution in Exchange 2000.