Reproductive interference (RI) occurs when individuals of one species display reproductive behaviour towards individuals of a different species that results in a loss of fitness for one or both species. These reproductive behaviours can take many forms, ranging from an overlap in sexual signalling, through to heterospecific courtship and mating attempts. In their 2008 review, Gröning and Hochkirch defined RI as “any kind of interspecific interaction during the process of mate acquisition that adversely affects the fitness of at least one of the species involved and that is caused by incomplete species recognition”¹. We argue that the second part of this definition, “caused by incomplete species recognition”, is unnecessary and may hinder progress exploring the importance of reproductive interference. First, processes such as “signal jamming” need not require species recognition failure. Second, determining if incomplete species recognition is the cause of RI will often be far from straightforward, as one has to prove a negative. Instead, we focus on the factors likely to influence the occurrence of RI and, most importantly, what the presence of RI between species can tell us about both the mating system of those species, and how natural and sexual selection have shaped those mating systems. We present a more holistic view of the interactions between ecology and mating system evolution, highlighting the processes that may be influenced by RI. We argue that the study of reproductive interference provides unique opportunities to further our understanding of sexual selection.