Romney: 'This is a time of great challenges'
Mitt Romney
Credit: Getty Images
Republican presidential candidate, Mitt Romney, speaks at the podium as he concedes the presidency at the Boston Convention & Exhibition Center. (Photo by Alex Wong/Getty Images)
Related:
Re-elected, Obama returns to divided government
Election over, US stocks dip on challenges to come 
Watch President Obama's victory speech
Obama: 'We have picked ourselves up,' fought back
Watch Mitt Romney's concession speech
Election night blog: Obama calls for unity
Photos: Americans get out and vote
Photos: Mitt Romney votes
Suspense to the end, both tickets in Cleveland
