Spin Glasses

The understanding of random magnetic systems known as spin glass has been one of the major challenges in condensed matter physics over that past two decades. Study of this state can be thought of as a rst step towards understanding more complex and disordered systems.This paper reviews some of the theoretical developmets in this eld and tries to answer the question how well are these systems understood.Some of the experi mental properties and a theoretical deenition of these system are introduced followed by a review of theoretical models.Emphasis is on meanneld theories and the statistical formulations needed to understand these systems.Some dynamical models and the applications of RG group and simulation methods follow this.The paper ends with the application of SG models to related systems in Physics and other elds especially biological systems.