Radio Frequency Identification (RFID) technology has experienced great success in recent years, with RFID tags becoming ubiquitous in our daily lives. The RFID market also bears witness to this, encouraging the development of systems able to identify, locate, authenticate, and engage billions of items connected to the Internet. Therefore, it is apparent that RFID systems are going beyond identification, by pushing the design of other capabilities, among which localization stands out. The spatial position of an item represents an added value of the system, which also fosters a potential Return-on-Investment growth. The accuracy of the localization system is strictly dependent on the item sizes and the application at hand, so many solutions can be implemented, each one with a proper trade-off among system complexity, algorithms running time, localization accuracy, and system reliability. Several parameters are available from off-the-shelf RFID hardware during the detection of passive tags, e.g., reading time, antenna detecting the tag, amplitude, and phase of the tag backscattered signal. The best way to deploy a high-accurate localization is typically based on the processing of multiple tag replies gathered in time, frequency, or spatial domain. The latter solution is the most reliable due to the limited available bandwidth in the standardized Ultra High Frequency RFID systems. This chapter will survey those methods and techniques where items equipped with a passive RFID tag are localized by exploiting a relative movement between the stationary tag and one or more mobile reader antennas. The achievable performance will be demonstrated through experimental data when such a relative movement is implemented by a handling system.