The president and Mrs. Bush are joined in the U.S. delegation by his father, former President George Herbert Walker Bush, former President Bill Clinton and Secretary of State Condoleezza Rice.
President Bush is the first sitting American president to attend a pope's funeral.
In 1979, when Jimmy Carter was president, Pope John Paul II was the first pope to visit the White House. Administration officials say Mr. Carter declined an invitation to join the U.S. delegation.
President Bush met the pope on three occasions, including a visit to the papal summer residence outside Rome. Pope John Paul II often criticized the U.S. invasion of Iraq and, during their last meeting in June, rebuked President Bush for U.S. abuses at the Abu Ghraib prison.
President Bush says understood the pope's objections because he was a man of peace who did not like war.
While in Rome, the president will meet with Italian President Carlo Ciampi and Prime Minister Silvio Berlusconi.