Submarine canyons are narrow but deep submarine valleys that extend for hundreds of meters. They represent the most impressive structures that shape the present morphology of passive continental margins. They can occur off the mouth of riversc the Tagus, Zaire, Amazon, and Orinoco in the Atlantic; the Indus in the Indian Ocean; and the Var, Rhone, and Ebro in the Mediterranean. Some are sometimes disconnected from any stream mouth such as the Nazar¿ canyon, off Portugal, despite that fact that it is close to the coast. Some were connected to a river mouth during lowstands of sea level, such as the Wilmington canyon in the northwest Atlantic, or the Blackmud canyon in the northeast Atlantic. This article discusses the morphology and recent activity of the Capbreton Canyon off the coast of France and Spain, and discusses some theories about its formation.