Will the world end on December 21, 2012 according to the Mayan calendar?

The date December 21, 2012 is arrived at via the Mayan calendar.

"On Dec. 21, 2012, it will display the equivalent of a string of zeros, like the odometer turning over on your car, with the close of something like a millennium. In Maya calendrics, however, it's not the end of a thousand years. It's the end of Baktun 13. The Maya calendar was based on multiple cycles of time, and the baktun was one of them. A baktun is 144,000 days: a little more than 394 years."1

So, the Mayan calendar operates on cycles and on 12/21/12 it is going to reset to zero and start again. It is not predicting an end to the world. It is simply a cycle of time which happens to fall on that date. Furthermore, different scholars have different opinions about what is the proper day that the Mayan calendar is supposed to end on -- though most agree it is the Dec. 21, date. 

Think of it like this.  We have a calendar that ends on Dec. 31.  Does that mean its the end of the world on that day?  Of course not.  We just start the calendar over again.  The same thing with the Mayan calendar.  It ends on 12/21/12 and starts over again on 12/22/12.

Their Long Count Cycle began in 3,114 B.C. with a 394 "year period known as Baktuns. Thirteen was a significant, sacred number for the Mayas, and they wrote that the 13th Baktun ends on Dec. 21, 2012."2  It is simply the end of their calendar cycle.