Simple Summary: An influential idea in animal ethics is that moral favouritism towards members of one's own species is a prejudice. This prejudice has been labelled 'speciesism', in analogy with racism and sexism. But not all ethicists subscribe to the view that speciesism is a prejudice. In fact, the tenability of speciesism is a topic of ongoing ethical debate. A recent exchange between Peter Singer and Shelly Kagan might leave the impression that this debate has essentially reached a stalemate, since the disputing parties rely on irreconcilable moral intuitions. In the present article, I argue that this impression is misleading. I highlight both philosophical and empirical research avenues that can help to move the speciesism debate forward, emphasizing that not all ethical intuitions about speciesism should be given equal weight. The article is part of the special issue 'Animal Ethics: Questioning the Orthodoxy'.Abstract: This article identifies empirical, conceptual and normative avenues to advance the speciesism debate. First, I highlight the application of Evolutionary Debunking Arguments (EDAs) as one such avenue: especially where (anti-)speciesist positions heavily rely on appeals to moral intuition, and EDAs have potential to move the debate forward. Second, an avenue for conceptual progress is the delineation of speciesism from other views in its vicinity, specifically from the view that biological differences between species are sometimes morally relevant ('species-relativism'). Third, if we adopt Singer's definition of speciesism, then a limitation of the current debate is that it is not obvious whether the core ethical principle that underlies anti-speciesist positions-the Principle of Equal Consideration of Interests-is widely applicable. Arguably, the interests of animals are often too dissimilar to establish what equal consideration amounts to. I underscore the need for integrating philosophical and empirical research, to come to terms with the extent to which the interests of members of different species are alike, and with the question of whether any dissimilarities might be morally relevant."Our inclination to treat humans as though we are special is no mere prejudice. Despite what Singer says, there is a significant philosophical view at work here-one worthy of careful further investigation." Shelly Kagan [1] (p. 20)"At the end of the day, no clear consensus has emerged-or, at best, this one: no rejoinder to Singer's attack on speciesism has convinced many besides its author, and the challenge remains." François Jaquet [2] (p. 2)