This book discusses the minimum description length (MDL) principle and its applications to statistical learning and signal/image processing. The authors have extensive experience in applying MDL to solve many scientific problems, and will apply this powerful methodology to a wider research community. There are three books and an edited volume in the market about MDL. All of them discuss the topic at a more fundamental and philosophical level, and at times could be hard for beginners to follow. This book aims to make MDL more accessible for the readers and stresses on the application side.