It's official — President Barack Obama and Vice President Joe Biden have been reelected to a second term.

A joint session of the U.S. Congress counted the electoral votes Friday and certified Mr. Obama the winner 332 to Republican Mitt Romney's 206.

Even though the outcome of the 2012 presidential race was known on election day in November, the U.S. Constitution requires Congress to count the electoral votes and certify a winner.

The process dates back to the early days of the United States before electronic communication when the outcome of presidential elections was unknown for months.

Each state has a certain number of electoral votes based on its population.