RFID tag location in a 3D environment is investigated. The location of the tag with unknown coordinates can be estimated with certain accuracy. However, accuracy can be improved using the knowledge based on measurement of additional reference tags with known location. This book studies the mathematical formulation and practical realization of location sensing using RFID tags. Deviating from the standard use of RFID technology which employs one tag reader to identify presence of tag, multiple tag reader with known location are used to estimate the physical location of an individual tag, with/without the help of few reference tag with known location. Additionally, concept of trilateration has also been extended for tracking the tag on unknown location without use of reference tags. It was demonstrated that both approaches were proved to be cost-effective technique and estimation of the location of a specific tag has been achieve with sufficient accuracy.