Rubicon Project is an online advertising technology firm based in Los Angeles, California. Its primary service is technology that optimizes advertising revenue for web sites. The company was founded in 2007, by Frank Addante, Craig Roah, Duc Chau and Julie Mattern who had previously worked together at L90 - an online advertising network.

By April 2009, the company had raised $33 million in venture funding led by Clearstone Venture Partners, IDG Ventures Asia and Mayfield Fund. The company also secured $8 million in venture debt from Silicon Valley Bank.

In May 2010, the company bought Site Scout, a malware detection company, although the company does itself place tracking cookies onto personal computers.

In October 2010, the company acquired Fox Audience Network from News Corp. in return for a minority stake in the company. It also received $18 million in additional funding led by Peacock Equity, the venture division of NBC Universal.

The Rubicon (Latin: Rubicō, Italian: Rubicone) is a shallow river in northeastern Italy, about 80 kilometres long, running from the Apennine Mountains to the Adriatic Sea through the southern Emilia-Romagna region, between the towns of Rimini and Cesena. The Latin word rubico comes from the adjective "rubeus", meaning "red". The river was so named because its waters are colored red by mud deposits. It was key to protecting Rome from Civil War.

The idiom "Crossing the Rubicon" means to pass a point of no return, and refers to Julius Caesar's army's crossing of the river in 49 BC, which was considered an act of insurrection. Because the course of the river has changed much since then, it is impossible to confirm exactly where the Rubicon flowed when Caesar and his legions crossed it.

During the Roman republic, the river Rubicon marked the boundary between the Roman province of Cisalpine Gaul to the north-east and Italy proper (controlled directly by Rome and its socii (allies)) to the south. On the north-western side, the border was marked by the river Arno, a much wider and important waterway, which flows westwide from the Apennine Mountains (its source is not far from Rubicon's source) into the Tyrrhenian Sea. Governors of Roman provinces were appointed promagistrates with imperium (roughly, "right to command") in their province(s). The governor would then serve as the general of the Roman army within the territory of his province(s). Roman law specified that only the elected magistrates (consuls and praetors) could hold imperium within Italy. Any promagistrate who entered Italy at the head of his troops forfeited his imperium and was therefore no longer legally allowed to command troops.