This book offers a new approach to the way in which biologists evaluate both the explanations they give of biological phenomena and those they would like to pursue. Departing from current scholarship on explanation, it draws out a cluster of virtues which unifies some biological explanations and, in turn, captures part of what makes the life sciences distinctive: integrative promise. With case studies drawn from a wide variety of historical and empirical domains (such as big data biology, model organisms, and natural history), as well as theoretical connections to a number of other areas in the philosophy of science (including mechanism, science and values, and scientific modeling), this work creates a new lens which helps us understand why contemporary life science takes the structure that it does. It provides insight for readers in philosophy and history of science, as well as biologists interested in the theoretical structure and future of their field.