This paper elucidates the social, ethical, cultural, technical, and legal implications / challenges around the implementation of a biometric based unique identification (UID) number project. The Indian government has undertaken a huge effort to issue UID numbers to its residents. Apart from possible challenges that are expected in the implementation of UID, the paper also draws parallels from Social Security Number system in the US. We discuss the setbacks of using the Social Security Number as a unique identifier and how to avoid them with the system being proposed in India. We discuss the various biometric techniques used and a few recommendations associated with the use of biometrics.