While at NCSA, Andreessen, along with Eric Bina, co-creates Mosaic, a user-friendly web browser that makes the internet accessible to a broader audience. Mosaic features an intuitive graphical interface, which simplifies web navigation.

Andreessen leaves NCSA and co-founds Mosaic Communications Corporation (later renamed Netscape Communications Corporation) with Jim Clark, the founder of Silicon Graphics.

Netscape quickly develops Netscape Navigator, a commercial web browser based on the principles of Mosaic. It becomes the dominant browser in the mid-1990s, significantly contributing to the internet boom.

Netscape goes public in a highly successful IPO, marking a pivotal moment in the dot-com era. The company's valuation soars, making Andreessen a prominent figure in the technology world.

Netscape faces intense competition from Microsoft's Internet Explorer in what becomes known as the 'Browser Wars'. Microsoft bundles Internet Explorer with Windows, challenging Netscape's dominance.

Facing increasing pressure from Microsoft, Netscape is acquired by America Online (AOL) for $4.2 billion. Andreessen briefly serves as Chief Technology Officer at AOL.