Privacy is increasingly important in the online world. Corporations, governments, and other organizations are realizing and exploiting their power to track users and their behavior. On the other hand, advances in hardware technology have lead to an increase in the capability to store and record personal data about consumers and individuals. This has lead to concerns that the personal data may be misused for a variety of purposes. In order to alleviate these concerns, we will study the different aspects of privacy-preserving technologies. Anonymity and unlinkability are the two required features that should be achieved to preserve privacy. Privacy breach may take place with or without a user's explicit participation. We will study both the cases.