A biometric system is essentially a pattern recognition system that operates by acquiring biometric data from an individual, extracting a feature set from the acquired data, and comparing this feature set against the template set in the database. Multimodal biometric systems are becoming more and more popular, they have more accuracy as compared to unimodal biometric systems. On the other hand these systems are more complex. We discuss here different types of multimodal biometric systems, different decision fusion techniques used in these systems. We discuss their feasibility and advantage over unimodal biometric systems & some of the future directions of biometrics system.