This is a book that fills the gap between Newtonian gravitation and sophisticated, relativistic theories. It will enable the advanced undergraduate or beginning graduate student to learn the postnewtonian theory that is necessary to account for precise, modern observations. No knowledge of differential geometry is assumed - the required, geometrical ideas are dealt with, as they arise, in their physical context. The book will be useful as an introduction to relativistic theories. Professional physicists and astronomers will be interested in the way the postnewtonian theory is derived as an almost trivial generalization of the Newtonian.