Barack Obama says he is a Christian, although he does not go to church. He was a member of the church where Jeremiah Wright was pastor, and Wright married Barack and Michelle and baptised their children.
Mitt Romney is Mormon, which formally is The Church of Jesus Christ of Latter-Day Saints. Mormons say they are Christian, but other Christians find some of their beliefs odd. Mormons are known for devotion to family.
Joe Biden and Paul Ryan are both Catholic.
One issue that divides them is abortion; Obama and Biden support a woman's right to choose abortion, while Romney and Ryan do not. Another issue is gay marriage, which Obama and Biden support, while Romney and Ryan oppose it.