The person and legacy of Thomas Aquinas enjoy great interest in contemporary scholarship, yet his thought eludes straightforward encapsulation, and adequate answers to the question "What is Thomism?" are difficult to find. In his aptly titled magnum opus, The Essence of Thomism, Gallus Manser, O.P., provides a precise and comprehensive reply to this question, explaining the genius of both the historical figure of Aquinas and the intellectual tradition that bears his name. First published in 1932, The Essence of Thomism was immediately hailed as a work of unusual erudition and insight. Rather than merely cataloging the characteristics of Thomistic thought, Manser elucidates the first principles of the synthesis that Aquinas bequeathed to posterity, masterfully surfacing the scientific and systematic vitality that has perennially informed the Thomistic tradition. Inspired by Aquinas's own unwavering pursuit of universal truth, Manser seeks to identify the unified formality and speculative soul of Thomism, exploring it from within and providing a guided tour of what lies at the heart of Thomistic thought.