  This Chapter outlines the replica approach in Random Matrix Theory. Both
fermionic and bosonic versions of the replica limit are introduced and its
trickery is discussed. A brief overview of early heuristic treatments of
zero-dimensional replica field theories is given to advocate an exact approach
to replicas. The latter is presented in two elaborations: by viewing the
$\beta=2$ replica partition function as the Toda Lattice and by embedding the
replica partition function into a more general theory of $\tau$ functions.
