This book is devoted to the mathematical description of interesting phenomena which occur in solids, such as ferromagnetism, antiferromagnetism and superconductivity. Superconductivity and its interaction with ferro and antiferromagnetism is of special importance since over the last 15 years the temperature of superconductivity existence has been raised from 15-20 K to 100 K, which will allow in the near future numerous practical applications of this phenomenon. Although the book is written in a rather rigorous mathematical language it is made easy to read by detailed derivation for those having only an undergraduate background in physics. Key Features: - new field of research- common formalism for superconductivity and magnetism- easy and simple models- easy reading which includes all derivations- good for graduate students and young researchers* A new field of research* Common formalism for superconductivity and magnetism* Easy reading and simple models, which includes all derivations