The Summa Theologiae, Supplementum Q. 1–99 presents the supplement material to St. Thomas Aquinas' Summa Theologaie. St. Thomas died before he could finish writing his magnus opus. Some of his friends and followers finished the Summa using material from the Saint's commentary on Peter Lombard's Sentences.

The Supplementum begins by finishing the treatise on penance, then investigates the sacraments of extreme unction, matrimony, holy orders, and then moves into eschatology with a treatise on the resurrection. Two further appendices composed of three questions total on purgatory follow after.

The Summa Theologiae is one of the greatest works of Christian theology ever written. Composed in the 13th century, it has inspired countless theologians, philosophers, saints and popes even today. The Supplementum is the fifth and final volume of Henderson Publishing's edition of the Summa Theologiae.