In recent years, much effort has been placed in solving the problem of speech recognition. The accompanying problem, that of speaker recognition, has received much less at tention. Speaker recognition is of importance in many commercial, military and forensic applications. Commercial applications include a variety of access control systems, credit card verification, E-commerce and more. This paper discusses the various types of speaker recognition systems, and presents the various available theoretical methods and algorithms. The various applications of speaker recognition systems are analyzed. Offline and online implementation problems and the appropriate solutions are presented. A detailed case study is discussed.