Mosaic is the common name of the first World Wide Web browser. It is a software application that was developed at the National Center for Supercomputing Applications (NCSA) in Urbana-Champaign, Illinois, by Marc Andreessen, Eric Bina, and others. Mosaic was the first cross-platform browser (available for the Macintosh, Windows, and UNIX all with the same interface) and became the precursor to Netscape, which officially started the popularity of the Web. It is copyrighted as "NCSA Mosaic," and the source code was licensed to several companies, including Netscape.

Mosaic has always been distributed as freeware. In 1994, however, the NCSA turned over commercial development of the program to a company called Spyglass. There are now several varieties of Mosaic, some free and some for sale.