Relay attacks generally occur between two entities that communicate with each other through wireless means. When a relay attack between a honest prover and a honest verifier occurs, an adversary tricks the prover and verifier into believing that they are indeed communicating with each other. Such attacks are rather difficult to identify and prevent since a passive adversary does not modify any of the communicated messages between prover and verifier. RFID/NFC-based applications are particularly vulnerable to such attacks. We provide an overview of RFID-based relay attacks and evaluate various streams of research that have attempted to address these attacks. Specifically, we consider distance-bounding techniques and the use of artificial or natural ambient conditions, with specific emphasis on the latter.