Proyecto 40 grew from a single station, XHTVM-TV in Mexico City, which signed on in 1995. XHTVM was originally majority-owned and operated by Javier Moreno Valle as CNI Canal 40, a news-oriented outlet.
On July 29, 1998, CNI partnered with TV Azteca, becoming "Azteca 40", TV Azteca's third station. Under this partnership, TV Azteca sold the advertising time and programmed 21.5 hours of the station's broadcast day; CNI retained 2.5 hours a day of programming. The partnership was broken off in 2000 when Moreno Valle turned on Azteca, alleging breach of contract. Azteca would take control of the station again in December 2002, when it used private security guards to forcibly take over the Cerro del Chiquihuite transmitter site, and again in 2005, after CNI shut down due to an employee strike and Azteca worked with minority owner Hernán Cabalceta to ensure it had the legal rights to broadcast. The current Proyecto 40 started broadcasting in early 2006.
Proyecto 40's programming under Azteca management currently consists of a mix of programming including newscasts, panel discussions, and general entertainment shows. TV Azteca and Showtime in the United States signed an agreement in September 2008 under which Proyecto 40 began to carry Dexter, Nurse Jackie and other Showtime programs.
Prior to 2012, Proyecto 40 could be seen throughout Mexico via cable or satellite television. Proyecto 40's over-the-air coverage was significantly expanded in November 2012, when Azteca 13 network stations across México began to carry it as a digital subchannel in high definition.
The following list is of all of Proyecto 40 affiliates as of November 2013.