Long buried in the archives of the Dominican studium at Le Saulchoir, the lectorate dissertation of Fr. Niels Krogh Rasmussen, OP, is now made available to a wider English-speaking audience interested in Saint Thomas Aquinas’s contribution to liturgical theology. Originally written in 1966, just after the Second Vatican Council, Rasmussen’s work is a witness to the intense liturgical ferment of those years and expresses an early attempt to appropriate the then-new postconciliar mode of liturgical reflection, bolstered by attentive historical-critical work, in the spirit of Saint Thomas. Treating the saint’s reflection on the Mass rites in the Summa Theologiae, Rasmussen shows how Aquinas, while writing in the disputed question format, nevertheless presents his readers with an expositio Missae, placing him within the tradition of great medieval Mass expositors, from Amalarius of Metz and Florus of Lyon in the ninth century, Saint Albert the Great and Durandus of Mende in the thirteenth century. By isolating this distinctly liturgical content (without, however, completely eschewing its original quaestio format), Rasmussen is able to highlight the distinctiveness of Thomas’s liturgical thought against that of his predecessors and contemporaries. Even if certain insights or expressions of Rasmussen’s may sound dated to the contemporary reader—since this work was composed in that interim period between Inter Oecumenici (1964) and the promulgation of the Missal of Paul VI (1969)—such insights in fact add to the historical value of this dissertation, offering a snapshot of a time when the reform of the liturgy was very much a living process with a terminus yet to be determined. 60 years later, students of Thomism, liturgical theology, and medieval studies can continue to benefit from this work.