Tim O'Reilly (Irish: Tadhg Ó Raghallaigh, 1954-) was born in Cork, Ireland. He is the founder of O'Reilly Media (formerly O'Reilly & Associates) and a supporter of the free software and open source movements. He is widely credited with coining the term Web 2.0.

O'Reilly was initially interested in literature upon graduating from high school, but after graduating from Harvard College in 1975 with a B.A. cum laude in Classics he became involved in the field of computer manuals. He defines his company not as a book or online publisher, or as a conference producer (though the company does all three), but as a technology transfer company, "changing the world by spreading the knowledge of innovators." O'Reilly is on the board of CollabNet, and was on the board of Macromedia until its 2005 merger with Adobe. In March 2007, he joined MySQL AB’s Board of Directors.

In 2001, O'Reilly was involved in a dispute with Amazon.com, blank">leading a protest against Amazon's _one-click patent, and specifically, Amazon's assertion of that patent against rival barnesandnoble.com. The protest ended with O'Reilly and Jeff Bezos visiting Washington D.C. to lobby for patent reform.

In December 2006, O'Reilly's publishing firm donated $10,000 to Creative Commons, demonstrating his interest in the Free Culture movement.

Tim O'Reilly is a singer/songwriter/guitarist who played bass guitar with the early-1980s Sydney-based psychedelic band Prince Vlad & the Gargoyle Impalers, played bass guitar and sang with the 1980s Australian indie rock band The Mexican Spitfires and later sang with the Australian gospel choir The Elementals.

Tim wrote two songs on The Mexican Spitfires debut record "Lupe Velez": "Town Hall Steps" (about Sydney Town Hall) and "Ivy Street" (about Ivy Street, Redfern — a street familiar to many students of Sydney University).

Tim's brother is Paul O'Reilly who was bass player for Sydney indie-rock band Women of Troy.