The most difficult challenge for naturalists in philosophy is accounting for scientific understanding of nature as itself a scientifically intelligible natural phenomenon. This book advances naturalism with a novel response to this challenge, drawing upon the philosophy of scientific practice and interdisciplinary science studies, philosophical work on the normativity of conceptual understanding, and new developments in evolutionary biology. The book’s two parts develop complementary, mutually supporting revisions to familiar accounts of conceptual understanding and of Sellars’s “scientific image” of ourselves-in-the-world. The first part shows how language and scientific practices exemplify the evolutionary process of niche construction. Conceptual capacities arise from the normativity of discursive practice within an evolving developmental niche, in place of familiar naturalistic appeals to a functional teleology of cognitive or linguistic representations. The second part treats scientific understanding (“the scientific image”) as situated within the ongoing practice of scientific research rather than as an established body of scientific knowledge. Scientific work does not culminate in a single, comprehensive image within the Sellarsian “space of reasons”; the sciences instead expand and reconfigure the entire space of reasons, in ways that are prospectively directed toward further revision in research. The first part thereby situates our conceptual capacities within a scientific conception of nature, while the second part explicates a scientific conception of nature in terms of that account of conceptual understanding.