Numerical methods are playing an ever-increasing role in physics and engineering. This is especially true after the recent explosion of computing power on the desk-top. This book is aimed at helping the user to make intelligent use of this power tool. Each method is introduced through realistic examples and actual computer programs. The explanations provide the background for making a choice between similar approaches and the knowledge to explore the network for the appropriate existing codes. Tedious proofs and derivations, on the other hand, are delegated to references. Examples of uncoventional methods are also given to stimulate readers in exploring new ways of solving problems.