On the Replica Approach to Spin Glass

In this talk I will review the approach to spin glasses based on the spontaneously broken replica symmetry. I will concentrate my attention mostly on more general ideas, skipping technical details and stressing the characteristic predictions of this approach. After the introduction of the replica method, the predicted structure of states is investigated in details, paying a particular attention to the local overlaps and to the structure of the clusters. I will finally study the behaviour of the system near the lower critical dimension and I will show that the technique of coupling real replicas is able to give relevant information.