The emerging technology of very inexpensive inertial sensors is available for navigation as never before. The book lays the analytical foundation for understanding and implementing the navigation equations. It starts by demystifying the central theme of the frame rotation using such algorithms as the quaternions, the rotation vector and the Euler angles. After developing navigation equations, the book introduces the computational issues and discusses the physical aspects that are tied to implementing these equations. The book then explains alignment techniques. Introduction to Modern Navigation Systems offers an efficient algorithm for polar navigation. It also shows how to enhance the performance of the inertial system when aided by the Global Positioning System. It is an appropriate textbook for senior undergraduate and graduate students in aeronautical and electrical engineering. It could also be used as a reference book for practitioners in the field.