- The Tzolkin, also known as the Sacred Round, was a 260-day calendar made up of 13 cycles of 20 days. Some researchers believe the Tzolkin was the first Maya calendar.
- The Haab, also know as the Vague Year, was made up of 18 months of 20 days plus an additional five-day period for a total of 365 days. According to the Maya World Studies Center, the Maya often described dates according to their position in the Tzolkin and the Haab calendars in a combined system known as the Calendar Round.
- The Long Count calendar was used by the Maya to track years over a long period. It began on approximately Aug. 13, 3114 B.C., and counts down more than 5,000 years to a zero date estimated to fall on Dec. 21, 2012. It then resets.
- At the city of Chichen Izta, in the present-day Mexican state of Yucatan, the Maya built a pyramid in the 11th century that serves as a calendar. The Pyramid of Kukulcan, also known as El Castillo, was constructed with four, 91-step staircases leading to a platform at the top. Add the total number of stairs and the platform, and the total is 365, the number of days in a calendar year.
- In 2006, author Daniel Pinchbeck published a book titled "2012: The Return of Quetzalcoatl" that sparked new interest in the Maya Long Count calendar by suggesting the calendar's zero date in 2012 "could herald the close of one way of existence and the beginning of another," according to the book's publicity material. Other books and articles have followed, capitalizing on the idea the Maya calendar predicts an apocalypse in 2012.
