Personal identity is the philosophical issue that deals with the problem of what makes a person persist over time. This inquiry takes root deep in the history of philosophy and the campaign to solve the problem never ceases. In the first section of this book I will provide a brief sketch of the issue, introducing important theories that contribute to the unraveling of the mystery. In section 2 and 3 respectively, the dominant two views---the physical approach and the psychological approach---will be examined in detail, and the difficulties confronting them will be presented, along with my comments on both views. I will, in the last section, propose my own solution to the problem, claiming that the sufficient and necessary condition for personal identity is neither physical continuity nor psychological continuity, but both. The work should serve as an introductory survey for those interested in this particular philosophical issue and help shed some light on the puzzle concerned.