George Polya & Robert E. Tarjan 
Notes on Introductory Combinatorics [PDF ebook] 

"This is a delightful little paperback which presents a day-by-day transcription of a course taught jointly by Polya and Tarjan at Stanford University. Woods, the teaching assistant for the class, did a very good job of merging class notes into an interesting mini-textbook; he also included the exercises, homework, and tests assigned in the class (a very helpful addition for other instructors in the field). The notes are very well illustrated throughout and Woods and the Birkhauser publishers produced a very pleasant text.One can count on [Polya and Tarjan] for new insights and a fresh outlook. Both instructors taught by presenting a succession of examples rather than by presenting a body of theory [The book] is very well suited as supplementary material for any introductory class on combinatorics; as such, it is very highly recommended. Finally, for all of us who like the topic and delight in observing skilled professionals at work, this book is entertaining and, yes, instructive, reading." Mathematical Reviews (Review of the original hardcover edition)"The mathematical community welcomes this book as a final contribution to honour the teacher G. Polya." Zentralblatt MATH (Review of the original hardcover edition)