  In this talk we review our theoretical understanding of spin glasses paying a
particular attention to the basic physical ideas. We introduce the replica
method and we describe its probabilistic consequences (we stress the recently
discovered importance of stochastic stability). We show that the replica method
is not restricted to systems with quenched disorder. We present the
consequences on the dynamics of the system when it slows approaches equilibrium
are presented: they are confirmed by large scale simulations, while we are
still awaiting for a direct experimental verification.
