Biometrics is the measurement of biological characteristics which are unique to an individual for identifying and verifying the individual. The measurements include fingerprints, retinal scans, iris scans, voice patterns, facial characteristics, palmprints, etc.., Biometric systems have been very much successful in identifying an unknown individual by searching a database of characteristics and by verifying the claim of an individual by comparing his characteristic with that stored in a database. To increase the robustness of the system and to make it more secure, multiple characteristics of the same individual are used. This is referred to as multimodal biometrics. In this paper we review some of the multimodal biometric systems.