This will be known as the end of the third millennium. In the sense of the Common Era calendar, the third millennium began on 1 January 2000 and will end on 31 December 2999. The majority of the celebrations for the start of the fourth millennium will presumably occur at midnight on 31 December 2999 / 1 January 3000. (2nd millennium – 3rd millennium – 4th millennium – other millennia) The third millennium is the third period of one thousand years in the Common Era. ... The Common Era (CE), also known as current era, is the period beginning with the year 1 onwards. ... (2nd millennium – 3rd millennium – 4th millennium – other millennia) The third millennium is the third period of one thousand years in the Common Era. ... 2000 is a leap year starting on Saturday of the Gregorian calendar. ... December 31 is the 365th day of the year (366th in leap years) in the Gregorian Calendar. ... January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... (29th century - 30th century - 31st century - other centuries) The 30th century (Gregorian Calendar) comprises the years 2901-3000. ...