PALO ALTO, Calif. — Marc Andreessen, an entrepreneur and software engineer behind the Web's earliest browsers, has joined the board of the online hangout Facebook.

Andreessen's appointment could bring additional clout and insight to a young but growing startup headed by Mark Zuckerberg, 24, who started Facebook as a Harvard undergraduate.

In a statement late Monday, Zuckerberg said Andreessen, 36, “has experience that is relevant to Facebook in so many ways: scaling companies that are experiencing extraordinary growth, creating successful technology platforms and building strong engineering organizations.”

Andreessen's appointment also brings him in alliance with a one-time rival. Microsoft Corp., whose Internet Explorer browser trounced Andreessen's Netscape in the 1990s, has invested $240-million for a 1.6 per cent stake in Facebook, giving the privately held company a $15 billion valuation.

Andreessen joins Zuckerberg, Jim Breyer of Accel Partners and Peter Thiel of Clarium Capital and Founders Fund on Facebook's board. David Sze of Greylock Partners and Paul Madera of Meritech Capital Partners are board observers.

Andreessen also is co-founder and chairman of Ning, a service for letting groups create their own social networks — potentially competing with Facebook, though Facebook described Ning's system as “complementary.”

Andreessen's involvement with the Web spans more than a decade.

In 1993, Andreessen and colleagues at the University of Illinois' National Center for Supercomputing Applications released Mosaic, the first Web browser to integrate images and sound with words. Previously, access was largely limited to text, with any graphics displayed in separate windows.

Andreessen and others soon left to commercialize the browser, and in 1994 they released the first version of Netscape. But Netscape's use eroded after Microsoft stepped into the market, and Time Warner Inc.'s AOL ultimately bought Netscape for $10-billion. Andreessen stayed on briefly as AOL's chief technology officer.