This is a text on the subject of superconductivity, an area of intense research activity worldwide. The book is in three parts: the first deals with phenomenological aspects of superconductivity, the second with the microscopic theory of uniform superconductors; and the third with the microscopic theory of nonuniform superconductors. This text will be of great interest to graduate students taking courses in superconductivity, superfluidity, many-body theory, and quantum liquids. It will also be of value to research workers in the field of superconductivity.