The Summa Theologica (1265 - 1274, Latin: Summa Theologiae) is a theological treatise of the thirteenth century, written by St. Thomas Aquinas during the last years of his life. The work was completed posthumously by his disciples. It is the most famous work of medieval theology and its influence on later philosophy is very broad, especially in Catholicism. Conceived as a manual for theological education, rather than as an apologetic work destined to polemicize against non-Catholics, it exemplifies the intellectual style of scholasticism in the structure of its articles. It is related in part to a previous work, the Summa Contra Gentiles, with more apologetic content.

In addition to the strictly religious sources (the Scriptures and the dogmatic definitions of the Catholic Church), St. Thomas relies on the work of some authors: Aristotle in philosophy and Augustine of Hippo in theology. Pedro Lombardo, theologian and author of the most used manual at the time, is also frequently quoted.

The Summa, written in Latin, is made up of questions about the topic, which are then divided into articles that seek to answer a series of questions.

The work is divided into three parts, of which the second is subdivided into two sections:

    I: First part: God one; God trine; the creation; the Angels; man and the cosmos, providence (119 issues).
    II-I Second part, first section: The human act. Passion, habit, virtue, sin. The old law, the new law, grace, merit. (114 questions).
    II-II Second part, second section: Theological virtues: faith, hope, charity. Cardinal virtues: prudence, justice, strength, temperance. Charisma States. (189 issues).
    III. Third part: Christ: Incarnation, life and passion. Sacraments: Baptism. Confirmation. Eucharist. Penance (90 issues, inconclusive).