Pervasive computing environments are driven by the vision of enabling users to access location-based services from virtually anywhere, at any time. This research vision requires systems that are able to continuously recognize a user's identity and location. Information about a user's identity allows us to tailor services to a user's preferences, and RFID tags enable us to determine the items a user is currently interacting with. RFID tags are small, inexpensive devices that can supply two types of information: their IDs and some associated possibly updatable information. This basic functionality of RFID tags is extremely flexible and enablling far-reaching applications. Our research focuses on RFID-based indoor localization techniques.