The fourth season of the American science fiction television series Star Trek: Enterprise commenced airing on the UPN network in the United States on October 8, 2004 and concluded on May 13, 2005 after airing 22 episodes. Set in the 22nd century, the series follows the adventures of the first Starfleet starship Enterprise, registration NX-01. The fourth season saw changes made to the production team, with Manny Coto becoming the show runner. He had joined the team during the third season as a co-executive producer. Other changes included Star Trek novelists Judith and Garfield Reeves-Stevens being brought on board as writers.

Enterprise (NX-01) is the fictional spaceship that serves as the primary setting of the American science fiction television series Star Trek: Enterprise. The ship predates the other Starfleet ships named Enterprise and was first seen in the pilot episode "Broken Bow". Its missions included an initial period of deep space exploration and a mission into the Delphic Expanse following the Xindi attack on Earth; it was also instrumental in the formation of the United Federation of Planets with the Vulcans, Andorians and Tellarites.