The attached file is a set of class notes developed by W.D. Nix of Stanford University and used in a graduate course on Mechanical Properties of Thin Films. These notes have been used in the graduate course MSE 353 since the late 1980's. That course has been taught every year or so since that time. The notes were last updated in January of 2005. The reader will see a note to the effect that many of the figures and illustrations in the file have been taken from the work of students and colleagues at Stanford without proper attribution. Those students and colleagues are hereby thanked for their contributions. The approach taken in developing these notes has been elementary and tutorial. No attempt has been made to create an authoritative treatise.Questions regarding these notes should be addressed to W.D. Nix at Stanford (nix@stanford.edu)