 (iii) Epistemic reduction is the idea that the knowledge about one scientific domain (typically about higher level processes) can be reduced to another body of scientific knowledge (typically concerning a lower or more fundamental level). While an endorsement of some form of epistemic reduction can be motivated by ontological reduction in combination with methodological reductionism (e.g., the past success of reductionist research in biology), the possibility of epistemic reduction does not follow directly from their conjunction. Indeed, debates about reduction in the  philosophy of biology  have centered on this third type of reduction as the most controversial issue (see  Section 4),  and therefore our discussion will focus primarily on issues related to epistemic reduction. Prior to evaluating any reduction of one body of knowledge to another, a conception of those bodies of knowledge and what it would mean for them to be  “reduced” must be explicated.  A number of different models of reduction have been proposed. Thus, the debate about reduction in biology has not only revolved around whether epistemic reduction is possible, but also which notions of epistemic reduction are operative in actual scientific reasoning. Two basic categories can be distinguished: (a) models of theory reduction maintain that one theory can be logically deduced from another theory  (Section 3.1);  and, (b) models of explanatory reduction focus on whether higher level features can be explained by lower level features  (Section 3.2).