The so–called “Sea Level Equation” is a linear, integral equation that governs the sea level changes due to the melting of the Pleistocene ice sheets and allows to model a suite of associated geophysical processes, including the postglacial rebound of the solid Earth, and the shape variations of the geoid. In this book we discuss the sea level equation for a spherically symmetric, linear viscoelastic Earth, assuming fixed shorelines and no rotational feedbacks. The theoretical aspects of the problem are presented in detail and only a basic knowledge of physics is demanded, that makes the discussion particularly oriented to non specialists of the field of global geodynamics. In the final part of the book we present some applications of the sea level equation in which we face the problem of predicting the Holocene and the present–day relative sea level variations, and the ongoing deformations of the solid Earth.