The study of the dynamics of satellites orbiting close to the Earth requires a careful investigation of the potential generated by our planet, to which we refer as the geopotential. This chapter is mainly devoted to the description of the geopotential, in particular its expansion in spherical harmonics, including the lowest order potential (the \(J_2\) problem), and some special cases, like that associated to axisymmetric bodies. We also discuss the effect of the atmosphere on the dynamics of satellites at low altitudes, which is very important and it must be included in the equations of motion.