The Expulso spellbook is a book containing information on and instructions how to perform the Expulso Curse.
It was owned by Dolores Umbridge in September of 1997 and was lying on her desk in her office, which she owned as Head of the Muggle-Born Registration Commission and Senior Undersecretary to the Minister for Magic at the Ministry of Magic. When Harry Potter came by it during the Infiltration of the Ministry of Magic he picked it up and learned the spell.
Behind the scenes
- It is possible that Umbridge confiscated the book during her tenure as the Hogwarts High Inquisitor in the 1995-1996 school year due to her dislike of practical magical instruction.