  This is an English translation of the Italian version of an encyclopedia
chapter that appeared in the Italian Encyclopedia of the Physical Sciences,
edited by Bruno Bertotti (1994). Following requests from colleagues we have
decided to make it available to a more general readership.
  We present the motivation for constructing General Relativity, provide a
short discussion of tensor algebra, and follow the set up of Einstein
equations. We discuss briefly the initial value problem, the linear
approximation and how should non gravitational physics be described in curved
spacetime.
