From “The Lowdown on Home-Buyer Tax Credits“:

Last week, President Barack Obama signed a law that extends through next spring a temporary tax credit of up to $8,000 for some first-time home buyers, which was due to expire Nov. 30. The law also adds a new tax credit of up to $6,500 for certain repeat home buyers. The package, which the government estimates will cost a total of $11 billion, is intended to help spur housing sales, a critical part of the economy.

There’s a good FAQ section in the article after this section.

More reading:
Homebuyers tax credit supported
Will rejuvenated tax credit draw more home buyers?
Extended Home Buyer Tax Credit May Not Be Good For Existing Buyers
Home Buyer Tax Credit Program Should Benefit Market, Realtors Say
The First-Time Homebuyer Tax Credit – A Consumer’s Point of View