Marc Lowell Andreessen (born July 9, 1971) is an American businessman, venture capitalist, and former software engineer. He is best known as co-author of Mosaic, the first web browser to display inline images; co-founder of Netscape; and co-founder and general partner of the Silicon Valley venture capital firm Andreessen Horowitz. As of June 2026, Forbes estimated his net worth at $1.9 billion.
Andreessen's career spans the early commercialization of the World Wide Web, enterprise software, and technology investing. He has been a prominent public advocate for technology innovation, including artificial intelligence and cryptocurrency, and has advised political figures, including Donald Trump from 2024.
Early life and education
Andreessen was born in Cedar Falls, Iowa, and raised in New Lisbon, Wisconsin. His father, Lowell, worked as a sales manager for seed producer Pioneer Hi-Bred International, and his mother, Patricia, was a customer service operator at Lands' End. He discovered programming at age 12 and later attended the University of Illinois at Urbana-Champaign (UIUC), where he earned a bachelor's degree in computer science in December 1993.
As an undergraduate, he interned twice at IBM in Austin, Texas, working on AIX graphics software, including the MIT X implementation and ports of 3D language APIs. He also worked as a programmer at the National Center for Supercomputing Applications (NCSA), earning $6.85 per hour (equivalent to $15.49 per hour in 2026). At NCSA, he became familiar with Tim Berners-Lee's open standards for the World Wide Web, though existing browsers required advanced programming skills to use.
After seeing the graphic web browser ViolaWWW in late 1992, Andreessen and full-time salaried co-worker Eric Bina developed Mosaic, a browser with integrated graphics that could run on Windows and other systems. Released in 1993, Mosaic led to a 342,000 percent increase in web traffic in a year. Before Mosaic, there were only 50 websites; afterward, the number grew to 10,000, and the percentage of internet users who surfed the Web rose from 1% to 25%. Mosaic is often called the first successful web browser, widely used on both Windows and Mac.
The NCSA refused to give the Mosaic team credit for their contribution, and a disillusioned Andreessen left the center in 1994.
Career
Netscape
After graduating, Andreessen moved to California to work at Enterprise Integration Technologies. He then met Jim Clark, founder of Silicon Graphics, who saw commercial potential in Mosaic. Together they founded Mosaic Communications Corporation in Mountain View, California, with Andreessen as co-founder and vice president of technology. The University of Illinois objected to the Mosaic name, so the company became Netscape Communications, and its flagship browser was named Netscape Navigator. Netscape was the first successful commercial web browser, offered for free, and it simplified the interface, increased speed, and supported financial transactions compared to Mosaic.
Netscape's IPO in 1995 brought Andreessen public attention, including a cover of Time magazine. Netscape was acquired by AOL in 1999 for $4.3 billion, with Andreessen's hiring as chief technical officer contingent on the deal. That year, he was named to the MIT Technology Review TR100 as one of the top 100 innovators under 35.
Opsware
After the AOL acquisition, Andreessen founded Opsware with Ben Horowitz, Tim Howes, and In Sik Rhee. Originally named Loudcloud, the company provided computing, hosting, and software services to internet and e-commerce firms. Loudcloud sold its hosting business to EDS and changed its name to Opsware in 2003, with Andreessen as chairman. Hewlett-Packard acquired Opsware for $1.6 billion in 2007. It was one of the first companies to offer software as a service and to attempt cloud hosting.
Andreessen Horowitz
Between 2005 and 2009, Andreessen and Horowitz invested $4 million in 45 startups, including Twitter and Qik, becoming known as super angel investors. On July 6, 2009, they announced their venture capital firm, Andreessen Horowitz, with an initial capitalization of $300 million. Within three years, the firm grew to $2.7 billion under management across three funds. Portfolio holdings included Facebook, Foursquare, GitHub, Pinterest, and Twitter. Successful IPOs that cemented the firm's reputation include Okta, PagerDuty, Pinterest, Slack Technologies, Lyft, DigitalOcean, and Coinbase.
Andreessen and the firm have shown strong interest in cryptocurrency. In 2021, they launched a $2.2 billion crypto-focused fund, followed by a $4.5 billion fund in 2022. Notable crypto and NFT startups in the portfolio include Alchemy, Dapper Labs, Avalanche, OpenSea, Solana, and Yuga Labs.
In 2023, the firm launched the American Dynamism fund, focusing on hard tech sectors serving national interest, including space, defense, manufacturing, and robotics. It has backed companies like defense manufacturing startup Hadrian and hypersonic rocket startup Castelion. In 2024, Andreessen Horowitz launched the American Dynamism Engineering Fellows Program to recruit and train technologists, and it sponsors an annual American Dynamism summit for startup founders.
Advocacy and public influence
Andreessen has been a vocal proponent of generative AI, arguing that it represents a transformative technological shift. His firm has invested in AI-related companies, and he has spoken publicly about the potential of large language models and machine learning. He has also been a prominent advocate for cryptocurrency and blockchain technology, viewing them as foundational to future internet infrastructure.
In 2024, Andreessen became an advisor to Donald Trump, reflecting his engagement with policy and political spheres. His public statements often emphasize optimism about technological progress and the role of entrepreneurs in driving economic growth.
Personal life and legacy
Andreessen has stated that he had problematic relationships with his parents and brother and did not like to discuss them. He has a younger brother named Jeff. Despite his early struggles, he became one of the most influential figures in technology, bridging the era of the early web and the modern AI and crypto investment landscape. His work on Mosaic and Netscape laid the groundwork for the commercial internet, and his venture capital firm has shaped the growth of numerous major technology companies.