The General Theory of Relativity, as it relates to navigation of spacecraft, can be separated into two parts. The first part involves derivation of a set of differential field equations that can be solved for the metric tensor. The second part involves inserting the metric tensor into the equation of geodesics to obtain equations of motion. In this chapter, the solution for the metric tensor is obtained from equations that provide a statement of the theory’s fundamental assumptions. The assumptions are simply that the speed of light is constant, matter or energy curves space, and the universe has some symmetrical properties. These assumptions are observed and cannot be proven. Two methods are used to solve for the metric tensor. The first is a computer solution that involves parameterizing the metric tensor and solving for the parameters using an orbit determination filter. The second is an analytic solution developed by Einstein by defining a covariant derivative and differentiating to obtain the Riemann tensor, Ricci tensor, and Einstein’s field equations, which can be solved for the metric tensor.