This paper discusses the impact of relaying in interference-limited networks by studying a two-user Gaussian interference channel with a relay (IeR). Various models for relay reception and transmission are possible: The relay can receive and transmit in the same band as the sources (i.e., in-band reflly reception! transmission), or else relay reception, or both reception and transmission, can take place over orthogonal links of limited capacity (i.e., out-of-band reflly reception or/ and transmission). In all scenarios, the selection of either signal refllying, interference forwarding or a combination thereof for the relay operation is identified as a common design choice. While signal relaying enables the destination to obtain a stronger desired signal or additional information, interference forwarding helps removing part of the interference. Important scenarios under which signal relaying and interference forwarding are optimal are identified, including cognitive relaying where the relay is unaware of the source codebooks and out-of band relaying, both under certain modified strong interference conditions and the latter under additional capacity constraints on the orthogonal relay links.