In the Introduction I outline the project of the book, the interpretation of several issues in the metaphysics of biology in terms of the notion of a philosophical stance. I proceed to discuss the concept of a philosophical stance (a cluster of values, attitudes, goals, commitments and beliefs) in general, then go on to distinguish epistemic stances—policies or strategies for forming beliefs, in particular regarding scientific ontology—from metaphysical stances—metaphysical positions construed as value-laden stances. I explain that these different types of stances play different roles in debates concerning metaphysical issues in science, and that this can be seen when we examine the stance-foundations of several issues in the metaphysics of biology, as I will be doing in the book.