MLB is controlled by the Major League Baseball Constitution that has undergone several incarnations since 1876 with the most recent revisions being made in 2005. Under the direction of Commissioner of Baseball (currently Bud Selig), Major League Baseball hires and maintains the sport's umpiring crews, and negotiates marketing, labor, and television contracts. As is the case for most North American sports leagues, the "closed shop" aspect of MLB effectively prevents the yearly promotion and relegation of teams into and out of the Major League by virtue of their performance.