"Regular Languages, Tree Width, and Courcelle's Theorem" provides an introduction to Courcelle's Theorem, a theorem about the complexityof deciding whether a finite mathematical structure satisfies a given logical formula. In this connection, further topics covered in the book include the interplay of logic and regular languages (e.g. Büchi's Theorem) and the graph theoretical concept of tree width, a measure of the similarity of a graph to a tree. The text assumes no previous mathematical knowledge of the reader other than some basic acquaintance with the concept of regular languages.