 Precise statements of what abduction amounts to are rare in the literature on abduction. (Peirce did propose an at least fairly precise statement; but, as explained in the supplement to this entry, it does not capture what most nowadays understand by abduction.) Its core idea is often said to be that explanatory considerations have confirmation-theoretic import, or that explanatory success is a (not necessarily unfailing) mark of truth. Clearly, however, these formulations are slogans at best, and it takes little effort to see that they can be cashed out in a great variety of prima facie plausible ways. Here we will consider a number of such possible explications, starting with what one might term the “textbook version of abduction,” which, as will be seen, is manifestly defective, and then going on to consider various possible refinements of it. What those versions have in common—unsurprisingly—is that they are all inference rules, requiring premises encompassing explanatory considerations and yielding a conclusion that makes some statement about the truth of a hypothesis. The differences concern the premises that are required, or what exactly we are allowed to infer from them (or both).