This volume investigates the concept of rationality as developed and debated within the philosophical and theological traditions of Judaism, Christianity, and Islam. It explores how each religion has drawn on, reinterpreted, or challenged philosophical understandings of reason—from classical Greek and Hellenistic thought to medieval scholasticism and modern critical philosophy. In Judaism, rationality is approached through rabbinic interpretation and medieval Jewish philosophy, where figures like Maimonides sought to reconcile revelation with reason. Christian thinkers, from Augustine to Aquinas and beyond, explored the role of rational inquiry in relation to faith, revelation, and natural law. Islamic philosophy developed complex models of rationality through kalām, falsafa, and Sufi metaphysics, with scholars such as al-Fārābī, Avicenna, al-Ghazālī, and Averroes engaging deeply with Aristotelian and Neoplatonic traditions. The volume highlights how rationality serves as both a tool of theological clarification and a means of ethical and metaphysical exploration, offering a rich comparative view on how reason shapes religious knowledge across traditions.