There are many differences between the Book and Movie. I'll be mentioning the major differences. This is part three, featuring the third book/movie of Harry Potter - The Prisoner of Azkaban
The Prisoner or Azkaban
1) In the movie, there was only one trip to Hogsmeade, while in the book there are two.
2) The friendship between Sirius and Crookshank's is completely omitted in the movie, but in the book it was mentioned.
3) Aunt Marge breaking the glass and her blowing up were in different meals in the book while in the movie it was in one big meal.
4) When Snape calls Hermione an "Insufferable Know-it-all", the book Ron defends Hermione while the movie Ron agrees with Snape.
5) In the book, Harry, Ron and Hermione jinx Snape at the same time in the Shrieking Shack, but in the movie, only Harry does so.
6) In the book, Harry doesn't study in the night undercover, but in the movie, he studies using Lumos Maxima. This should earn him a warning from the Ministry of Magic, but it doesn't.
7) In the book, Professor Trelawney's prediction happens after the Divination finals, but in the film it just happens after a random class.
8) In the book, Snape finds every opportunity to bully the trio, while in the movie he doesn't waste any time in unnecessary punishments (mostly).
9) In the book, the temporary enmity between Ron and Hermione is highlighted very well. In the movie, this whole part was omitted.
10) Helping Hagrid with Beakbuck's case was what made Ron and Hermione friends again in the book, but in the movie, this is not needed and is removed.
11) Many things like Ron getting a new owl, wand etc. are omitted in the movie and they appear in the next films without explanations.