R. de la Llave A tutorial on KAM theory (499K, LaTeX 2e) ABSTRACT. This is a tutorial on some of the main ideas in KAM theory. The goal is to present the background and to explain and compare somewhat informally some of the main methods of proof. It is an expanded version of the lectures given by the author in the AMS Summer Research Institute on Smooth Ergodic Theory Seattle, 1999. The style is pedagogical and expository and it only aims to be an introduction to the primary literature. It does not aim to be a systematic survey nor to present full proofs. It only covers the classical results and not the most modern ones. Comments and suggestions for improvement are welcome. We are planning a revised and expanded version.