Andreessen Horowitz (also known as a16z) is an American privately-held venture capital firm headquartered in Menlo Park, California, United States. It was founded in 2009 by Marc Andreessen and Ben Horowitz. The number "16" in the name comes from the letter count between the first letter in Andreessen and the last letter in Horowitz.

Andreessen Horowitz invests in both early-stage startups and established growth companies. Its investments span the healthcare, consumer, cryptocurrency, gaming, fintech, education, and enterprise software (including cloud computing, security, and software as a service) industries.

Between 2006 and 2010, Marc Andreessen and Ben Horowitz actively invested in technology companies. Both separately and together, they invested $4 million in 45 startups, including Twitter. During this time, the two became known as "super angel" investors.

On July 6, 2009, Andreessen and Horowitz launched their venture capital fund with an initial capitalization of $300 million. In November 2010, at a time when the field of venture capitalism was contracting, the company raised an additional $650 million for a second venture fund. In less than two years, the firm was managing a total of $1.2 billion under the two funds.

As of March 27, 2014, the firm was managing $4 billion in assets following the closing of its fourth fund at $1.5 billion.

By 2012, Business Insider wrote that, "Andreessen Horowitz is the most powerful and respected venture capital firm in Silicon Valley right now." The firm is often cited as the largest and one of the most powerful venture capital funds in the world. Marc Andreessen in particular is often cited as one of the most powerful venture capitalists, who is dominant, if also controversial, not only in Silicon Valley, but also in politics.

As per the website OfficeChai's calculations (up to October 2025), since 2020, Andreessen Horowitz has backed 32 unicorns, more than any other venture firm. By November 2025, Andreessen Horowitz's website lists 1076 portfolio companies. The note reads: "Any investments or portfolio companies mentioned, referred to, or described on this page are not representative of all investments in vehicles managed by a16z and there can be no assurance that the investments will be profitable or that other investments made in the future will have similar characteristics or results.

Exits include current and former a16z portfolio companies which have been acquired as well as companies which have undergone an initial public offering or direct public offering of shares. Certain publicly traded companies on this list may still be held in Andreessen Horowitz funds." The American Dynamism section lists 50 companies.

Leslie Feinzaig writes on Fast Company that nowadays Andreessen Horowitz and other big firms do not act like traditional venture capital firms anymore, but invest beyond early-stage private companies, including public equities, crypto tokens, non-traditional assets, and more. There is also a tendency towards competing for the obvious alpha, and not just making the contrarian's bet.

In 2023, the firm launched a $600 million American Dynamism fund "with the broad aim of supporting companies building in the nation's interest". American Dynamism has raised two funds since its establishment, with a total value of $1.8 billion. The fund focuses on hard tech sectors which serve national interest, including space, defense, manufacturing, robotics. In 2024, Andreessen Horowitz launched the 12-month American Dynamism Engineering Fellows Program, which was intended to recruit and train technologists.

Also associated with the American Dynamism fund is the annual American Dynamism summit sponsored by Andreessen Horowitz, which gathers startup founders, investors, Members of Congress and Defense Department officials. The summit is officially non-partisan and has partnered with Democratic defense officials like former Deputy Secretary of Defense Kathleen Hicks.

The fund has been managed by three general partners, namely Katherine Boyle, David Ulevitch and Erin Price-Wright. In July 2026, Connor Love was added to the team. David Ulevitch is the leader.

Boyle plays an important role in the initiative. She declares in an essay titled "Building American Dynamism" that, "I believe the only way to reverse the course of stagnation and kick-start nationwide renewal post-Covid is through technologists building companies that support the national interest." She had previously interned at Founders Fund and is influenced by Peter Thiel's thinking. In 2016, she joined General Catalyst where she helped fund Anduril, before joining Andreessen Horowitz.

Her portfolio at Andreessen Horowitz includes Hadrian, Apex Space (satellites) and Castelion (hypersonic weapons).

In 2009, Andreessen Horowitz made its first two investments: one in business management SaaS developer Apptio and one in Skype stock.

According to Horowitz, the Skype investment was seen as risky by other experts in the field, who believed the company would be crippled by ongoing intellectual property litigation and direct competitive attacks from Google and Apple. The firm's founders viewed the investment as a success following Skype's sale to Microsoft in May 2011 for $8.5 billion.