With the growing interest in the use of symmetry methods in applied mathematics, this book presents a comprehensive overview of the differential geometric view of the subject. The authors begin with a background chapter on calculus on manifolds, and then proceed to more advanced topics and applications, especially concerning singularities of the Monge-Ampere equations that describe many phenomena in geophysical fluid dynamics, for example. The authors describe many application areas and include computer code for implementing some of the techniques they describe. The book is richly illustrated.