Back in 1992, Visual SourceSafe (VSS) was considered state-of-the-art technology. Since then, as technology has rapidly advanced, development teams have generally grown in both size and complexity. Visual Studio Team Foundation Server (TFS) is the replacement for VSS and provides the very best collaboration tool for today's software development teams. TFS is much more than version control! It provides inreased scalability, improved collaboration and dramatically better tracking, ensuring that your development projects are more streamlined and efficient.
Here's a video that features the Founder of VSS and TFS as he describes the evolution of both tools in his own words: http://www.microsoft.com/visualstudio/en-us/upgrade-visual-sourcesafe