Secure and robust authentication is the key requirements for today's growing world of information and technology. High data security with ease of use is one of the key requirements for security systems today and biometric technologies provide several advantages over conventional systems which make them highly acceptable by individuals worldwide. A comprehensive study of the various existing biometric modalities has been discussed in this paper with some of the modern challenges and various key features to be kept in mind while choosing any biometric for a certain application. The different parameters used for performance evaluation of a biometric system are also discussed.