NCSA Mosaic is a discontinued web browser, and one of the first to be widely available. It was instrumental in popularizing the World Wide Web and the general Internet by integrating multimedia such as text and graphics. It was named for its support of multiple Internet protocols, such as Hypertext Transfer Protocol, File Transfer Protocol, Network News Transfer Protocol, and Gopher. Its intuitive interface, reliability, personal computer support, and simple installation all contributed to its popularity within the web. Mosaic is the first browser to display images inline with text instead of in a separate window. It is often described as the first graphical web browser, though it was preceded by WorldWideWeb, the lesser-known Erwise, and ViolaWWW.

Mosaic was developed at the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana–Champaign beginning in late 1992. NCSA released it in 1993, and officially discontinued development and support on January 7, 1997.

Starting in 1995, Mosaic lost market share to Netscape Navigator and only had a tiny fraction of users left by 1997, when the project was discontinued. Microsoft licensed Mosaic to create Internet Explorer in 1995.