Ellipsometry is an experimental technique for determining the thickness and optical properties of thin films. It is ideally suited for films ranging in thickness from sub-nanometer to several microns. Spectroscopic measurements have greatly expanded the capabilities of this technique and introduced its use into all areas where thin films are found: semiconductor devices, flat panel and mobile displays, optical coating stacks, biological and medical coatings, protective layers, and more. While several scholarly books exist on the topic, this book provides a good introduction to the basic theory of the technique and its common applications. The target audience is not the ellipsometry scholar, but process engineers and students of materials science who are experts in their own fields and wish to use ellipsometry to measure thin film properties without becoming an expert in ellipsometry itself.