This site documents everything that is known about keeping time on Mars. It documents more than 80 Martian calendars for defining the date on Mars and more than 40 Martian clock systems for keeping time on Mars. The earliest known Martian calendar was described in Percy Greg's 1880 utopian novel, Across the Zodiac. Another early Martian calendar was the joint invention of A. E. Douglass and W. H. Pickering, original members of the staff at Lowell Observatory in Arizona. Edgar Rice Burroughs' description of a Martian calendar in several of his novels were inaccurate and mutually inconsistent. The first accurate Martian calendar, complete with weeks, months, and a starting point of the calendar year, was developed in 1936 by Robert G. Aitken, director emeritus of the Lick Observatory in California. The first operational Martian timepiece was designed in 1954 by I. M. Levitt of the Fels Observatory in Philadelphia; it displayed the time and date on Earth, as well as the time on Mars and the date on Mars as defined by a Martian calendar of his own invention. This site documents more than 80 Martian calendars and more than 40 Martian clock systems for showing the time on Mars. A Martian calendar becomes more necessary as more robotic probes are sent to Mars and the human telepresence on Mars becomes more extended and sustained.