Cuarto Milenio deals with any subject related to the world of mystery and the unknown, among which are: conspiracy, occultism, criminology, astronomy, ufology, psychology, parapsychology, demonology, archeology, history, zoology or physics. The show usually has the participation of scientists and experts in various fields such as psychiatrists, physicists, historians, anthropologists, criminologists, astronomers, naturalists, writers or journalists. Directed and presented by journalists Iker Jiménez and Carmen Porter, they have been added to the Spanish network Cuatro, since November 2005. From the beginning, they had a "brother" radio program called Milenio 3 (which began on June 1, 2002 and ended on June 28, 2015) and captained by the same team, in Cadena SER.