The Mayans, developers of an ancient Amerindian civilization in Central America, employed three separate, overlapping, calendrical systems called by scholars the long count, the haab, and the tzolkin. Their civilization reached its zenith during the period 250-900 c.e., and theMayans survive to this day in Guatemala and in the Yucatan peninsula of Mexico and Belize; some groups have preserved parts of the calendar systems. What is known today has been recovered through astroarcheological and epigraphic research (see, for example, [10]). There is general agreement on the Mayan calendrical rules and the correspondence between the three Mayan calendars; however, the exact correspondence between the Mayan calendars and Western calendars is still a matter of some slight dispute (see [1]). Correspondences are proposed by date equivalences in Spanish sources and by interpreting Mayan recordings of astronomical phenomena, such as new moons. Here we give the details for the most popular (and nearly universally accepted) correspondence, the Goodman-Martinez-Thompson correlation [20]. Another correlation was used by Spinden [17], [18], [19]. A superb discussion of Mayan mathematics, astronomy, and calendrical matters was given by Lounsbury [9] (see also [8]).