Flock is a discontinued web browser that specialized in providing social networking and Web 2.0 facilities built into its user interface. Earlier versions of Flock used the Gecko HTML rendering engine by Mozilla. Version 2.6.2, released on January 27, 2011, was the last version based on Mozilla Firefox. Starting with version 3, Flock was based on Chromium and so used the WebKit rendering engine. Flock was available as a free download, and supported Microsoft Windows, Mac OS X and, at one time, Linux as well.

Support for Flock was discontinued in April 2011.

Flock was the successor to Round Two, who raised money from Bessemer Venture Partners, Catamount Ventures, Shasta Ventures and other angel investors. Bart Decrem and Geoffrey Arone co-founded the company. Flock raised $15 million in a fourth round of funding led by Fidelity Ventures on May 22, 2008, for an estimated total of $30 million, according to CNET. The company's previous investors, Bessemer Venture Partners, Catamount Ventures, and Shasta Ventures, also participated in the round.

In January 2011, Flock Inc. was acquired by Zynga. The browser has been discontinued, with support ending April 26, 2011.

Flock 2.5 integrated social networking and media services including MySpace, Facebook, YouTube, Twitter, Flickr, Blogger, Gmail, Yahoo! Mail, etc. When logging into any of the supported social services, Flock could track updates from friends: profiles, uploaded photos, and more. Flock 2.5 added Twitter Search functionality, multi-casting of status updates to multiple services, and the introduction of instant messaging via Facebook Chat in the browser.

Other features include:

In December 2007, Flock won the Mashable Open Web Awards for Applications and Widgets and in March 2008, Flock won the South By Southwest Web Award for Community.

CNET gave the Mac OS X version of Flock 1.0 the title of "Best Mac Software of 2007". PC World's Harry McCracken reviewed Flock as his "New Favorite Web Browser".