This book presents the fundamentals of orbit determination - from weighted least squares approaches (Gauss) to today's high-speed computer algorithms that provide accuracy within a few centimeters. Numerous examples and problems are provided to enhance readers' understanding of the material. It covers such topics as coordinate and time systems, square root filters, process noise techniques, and the use of fictitious parameters for absorbing un-modeled and incorrectly modeled forces acting on a satellite. It contains examples and exercises which serve to illustrate the principles throughout each chapter. It includes detailed solutions to end-of-chapter exercises available to instructors.