Nicholas Pileggi wrote "Wiseguys," on which "Goodfellas" is very closely based. Basically, only names are changed, and not all of them. Henry Hill and Karen maintain their real names in the book and the film. All the others have their names changed (i.e., Paul Vario in the book becomes Paulie Cicero in the film). The same approach is used in another Pileggi book, "Casino," which was made into a movie of the same name.