RFID is an automatic identification technique that stores and remotely retrieves data on small devices called tags. This technology enables tracking of people and objects and could support the conception of pervasive networks if identities are linked in real-time to their locations. We propose a scalable and robust 3-D localization method for RFID tags based only on connectivity information. Virtual landmarks are used to define inclusive and exclusive constraints, localize tags and estimate the accuracy of the calculations. Simulation results show that our algorithm provides fine-grained localization accuracy.