This book provides a thorough development of ridges and their application to image and data analysis. The text is self-contained by including a chapter on the necessary mathematical background, chapters on the formal ridge definitions in any geometric setting, and a chapter on the numerical implementation. An applications chapter covers three separate topics: medical image analysis, molecular modeling, and analysis of fluid flow. Audience: The book is intended primarily for computer vision and image processing scientists with a background in mathematics and scientific computation. However, ridges provide a general purpose tool for multidimensional data analysis, so the book will be of interest to practitioners in any field which requires the analyzing of data, such as statistics, the physical sciences, or engineering.