Will the 21st century begin Jan. 1, 2000 or 2001?
The 21st century begins in 2001.
Here's how to visualize it: A century consists of 100 consecutive calendar years. The 1st century AD consisted of the year 1 through 100. The 20th century consists of the year 1901 through 2000. So the last day of the 20th century will be Dec. 31, 2000.
But it may be a near-impossible job to convince all those people on New Year's Eve welcoming in the year 2000 that it's not really the turn of the century.