Another Fine Myth by Robert Asprin

Another Fine Myth is the first in the series of Myth Adventures books by Robert Asprin. It would fall into the category of humorous fantasy with some contemporary and science fiction elements intertwined. It follows the adventures of a magician's apprentice named Skeeve from the dimension of Klah (a Klahd) and a demon named Aahz from Perv (a Pervect, often mispronounced Pervert by others). They adventure out in the world to try to get Aahz's magical powers back and to battle another magician named Isstvan. In the course of their adventures they meet a number of interesting characters and interact with each other in hilarious ways. The book is excellent humorous fantasy that will have you laughing out loud at times and is a good break between more serious books. There are quite a few books in this series at it approaches 20 volumes and the first 12 or so have recently been released in large two volume collections with the second volume coming out in just a few days. The author uses a lot of puns and miscues and plot twists to humorous effect and the ability for the characters to travel to other worlds, or dimensions, enables multi-world capers of an unusual quality to take place.