Year zero
Year zero does not exist in the anno Domini system usually used to number years in the Gregorian calendar and in its predecessor, the Julian calendar. In this system, the year is followed by . However, there is a year zero in astronomical year numbering (where it coincides with the Julian year ) and in ISO 8601:2004 (where it coincides with the Gregorian year ) as well as in all Buddhist and Hindu calendars.
Missing years (Jewish calendar)
Today, Hebrew dating places the creation of the world near the end of "Year One" AM and afterwards the first year of Adam's life as "Year Two" AM. However, Seder Olam Rabba shows that the Hebrew dating originally counted the first year of Adam's life as "Year Zero" AM. This may mean that the Hebrew dating has shifted in the course of history such that traditional dating of ancient events appears two years earlier than the modern Hebrew dating would be.