The history of calendars spans several thousand years. In many early civilizations, calendar systems were developed. For example, in Sumer, the birthplace of the modern sexagesimal system, there were 12 months of 29 or 30 days apiece, much like the modern Gregorian calendar. Mesoamerican cultures also developed their own intricate calendars; the ancient Maya had two separate years—the 260-day Sacred Round, and the 365-day Vague Year. Classical Greek and Roman cultures also developed calendars; the ancient Athenians, for one, had a lunisolar calendar that lasted 364 days, with an intercalary month added every other year. The Romans used two different year lengths; the older one had 304 days divided into 10 months; the newer 365 days divided into 12 months; very much like the modern calendar. They counted years from the founding of Rome, or, sometimes, from the reign of the current consul. The Hindu calendar is known from texts from about 1000 BC and divides an approximate solar year of 360 days into 12 lunar months of 27 or 28 days. The resulting discrepancy was resolved by the intercalation of a leap month every 60 months. The Islamic civilization also developed their own calendar based of the moon.

The oldest known Calendar is a Lunar Calendar in Aberdeenshire, Scotland, which was constructed around 8,000 BCE.