The online world is undergoing a personalization renaissance. New technologies have been developed that allow online services to achieve true one-to-one personalization. Consumers are recognizing that they need personalization to help them manage the torrent of information available to them. And, online services are realizing the benefits it can deliver in terms of reducing churn and increasing sales. This paper outlines the basic components of a personalization system and reviews the strengths/weaknesses of three popular personalization technologies.