Today most applications are based on the secure accessing of openings to buildings, computer networks, laptops, cellular phones, bank transactions and ATMs. The aim of biometric recognition system is to ensure that the available services are utilized only by a legitimate user, or somebody else. This paper gives on overview of biometric recognition systems. It starts with the basic modalities taken for biometric system, and discusses about the procedure about how to recognize the person and various literatures and methodologies taken by many authors and the metrics to verify the recognition. The fusion methods adapted for biometric recognition plays an important role. All the fusion techniques which have been done on the particular biometric traits were discussed. Finally the normalization methods and the metrics used for evaluating the biometric system are discussed.