0 (year)

There is no year 0 in the Gregorian calendar. The year 1 BCE immediately precedes 1 CE. This is because when the system of numbering the years prior to the start of the era in the Julian calendar was devised, the number 0 had not yet been introduced to Europe.

Confusion over this fact, and a preference for anniversaries in "round" figures, led to the celebration of the millennium both in 2000 and 2001.

The year 0 is used in astronomical year numbering and is equivalent to 1 BCE in the Gregorian calendar.

Year Zero was the officially calendar designation of 1975 by the Khmer Rouge regime when they seized control of Cambodia.