This collection of essays by a distinguished mathematician and teacher examines important issues of dynamics from the viewpoint of the theory of functions of the complex variable. Based on a series of lectures delivered by Felix Klein in conjunction with Princeton University’s 150th anniversary, these presentations center on the problem inherent in the motion of a top—that is, a rigid body rotating about an axis—when a single point in this axis other than the center of gravity is fixed in position. The contents of this volume render discussions of dynamics-related issues simpler, more attractive, and relevant not only to mathematicians but also to engineers, physicists, and astronomers. Unabridged republication of the classic 1897 edition.