The Mostow Rigidity Theorem implies that Volume is actually a topological invariant for hyperbolic manifolds. In this talk we give an outline of Gromov’s proof of Mostow Rigidity for hyperbolic 3-manifolds. The proof uses the Gromov norm, which is a pseudo-norm on the homology of a topological space. If time permits, we will discuss theorems about the set of volumes of hyperbolic manifolds.