Spin glass theory is really one of the most fascinating and appealing topics in theoretical and statistical physics. Since the oldest paper in 1959, such systems, which appearently are neither ferromagnetic nor antiferromagnetic, have been studied far and wide, but a full and complete understanding of the transition of disordered systems is still missing. The physical reason of their complexity is that the free energy at low temperature occurs as a rough landscape with a huge number of metastable states and the conventional statistical techniques fail.