Appears in collection : 2015 - T1 - Disordered systems, random spatial processes and some applications

A self-contained review will be given about the equilibrium and off equilibrium properties of statistical mechanics systems, both in the case of ferromagnetic and disordered ones. A systematic use of interpolation arguments and convexity will be the main tool. The case of mean field will be treated throughly. The possible extensions to short range interaction will be pointed out.