From the Office of the Federal Register:
<< If no presidential candidate wins a majority of electoral votes, the 12th Amendment to the Constitution provides for the presidential election to be decided by the House of Representatives. The House would select the President by majority vote, choosing from the three candidates who received the greatest number of electoral votes. The vote would be taken by State, with each State delegation having one vote. If no Vice Presidential candidate wins a majority of electoral votes, the Senate would select the Vice President by majority vote, with each Senator choosing from the two candidates who received the greatest number of electoral votes. >>