President Barack Obama is trying to fend off a strong, late challenge in Pennsylvania by Republican nominee Mitt Romney. Democrats have won the past five presidential elections there.
Underscoring the state's importance and the aggressive fight for its prized 20 electoral votes, Romney is set to make an Election Day stop in Pittsburgh.
Pennsylvanians will also decide contests for Congress, attorney general, treasurer, auditor general and most state legislative seats. Polls open at 7 a.m. and close at 8 p.m.
Nearly 8.5 million voters are registered in Pennsylvania.