This edition contains several new areas of application, in chapter 4, many new problems and solutions, a number of improvements in the presentation, and corrections. It also contains an Appendix that describes some of the features of computer algebra programs that are of particular importance in the study of generating functions. I am indebted to many people for helping to make this a better book. Bruce Sagan, in particular, made many helpful suggestions as a result of a test run in his classroom. Many readers took up my o®er (which is now repeated) to supply a current errata sheet and my thanks in return for any errors discovered.