The intelligibility of nature was a persistent theme of William A. Wallace, OP, one of the most prolific Catholic scholars of the late twentieth century. This Reader aims to make available a representative selection of his work in the history of science, natural philosophy, and theology illustrating his defense and development of this central theme. Wallace is among the most important Galileo scholars of the past fifty years and a key figure in the recent revival of scientific realism. Further, his long and productive scholarly career has been shaped by a continuous effort to bring the resources of the Aristotelian-Thomistic tradition to the solution of contemporary problems of philosophy and science. Through all of these contributions, Wallace has provided the foundation for a renewed confidence in the capacity of human knowers to attain understanding of the natural order. Consequently, the overall aim of this volume is to secure continued access to his scholarship for readers in the new millennium. Intelligibility of Nature contains twenty-nine previously published essays written by Wallace over a period of some forty years. Many of these essays are currently not readily accessible. They are arranged in five thematic groups, each representing a major subject-area of Wallace's scholarly interests. The first group is devoted to essays on making nature intelligible through the use of scientific models. The second group of essays investigates various ways in which the Aristotelian-Thomistic tradition is foundational to contemporary scientific research. Essays in the third group are historical studies on the origins of modern science. The fourth group of essays discuss the viability of the cosmological argument for the existence of God in light of natural science. The final group of essays consider the relation of science and religion. Together these essays provide a representative sample of Wallace's multifaceted contributions to scholarship.