BOOK: Olivetti was the chief of the Vatican Swiss Guard. Richter was not on the novel.
MOVIE: Cardinal Baggia survived and became the Pope.
BOOK: All four cardinals (the Preferitti) died in the four churches that represents the altars of science, Earth, Air, Fire and Water.
MOVIE: The Assassin died because of the bomb planted on his car.
BOOK: Robert and Vittoria fought the Assasin and he died after falling from Castel Sant' Angelo.
The movie also eliminated the fight on Piazza Navona and on the Castel Sant' Angelo.
MOVIE: Vittoria stayed on the Vatican after one of the Cardinals was found on the Saint Peter's Square.
BOOK: Langdon fell in love with Vittoria and felt the rage when the Assassin caught her.
The movie eliminated the romantic flavor on the book.
MOVIE : Richter was the one who was falsely accused as Illuminatus.
BOOK : It was Maximilian Kholer, CERN director, who tried to kill the
BOOK: The antimatter just exploded above and the people only saw light from heaven.
MOVIE: The antimatter exploded high above the sky and brought about a blast on the St. Peter's Square.
I have to commend the movie for this. The book was a bit unrealistic considering the fact that the supposed antimatter would be enough to wipe the entire Vatican.
MOVIE: Langdon was on the ground when the antimatter exploded.
BOOK: Langdon ride the helicopter with Camerlengo and jumped just a few moments before the detonation. He fell on the Tiber river and was taken to the hospital.
I also commend the movie for removing this unrealistic scene.
The list above were just the major differences I remembered/noticed. There are other differences like names, roles, who say this and that. Please comment if you want to say something about this article or if you want to add another difference that you saw.