For the first time, the Russian reader is offered a complete translation of the treatise "On the Trinity" by the outstanding medieval thinker St. Augustine Aurelius (Blessed). As Augustine himself reported in a letter to Pope Aurelius (papae Aurelio), Bishop of Carthage in 416, " I started writing books about the Trinity as a young man, and I published them as an old man. This is not surprising, because the thinker wrote "On the City of God" for 15 years, "On Christian Teaching" for 30 years. This work ("On the Trinity") in its meaning is on a par with such works of the theologian as "Confession" and "On the City of God," and is devoted to the systematic presentation of Trinitarian issues, in which Augustine saw the basis of Christian doctrine. Starting with the exegetics of the texts of Holy Scripture, Augustine defends the dogma of trinity from a philosophical point of view, using analogies with the natural world and especially with the forms of activity of the human mind. The text of the treatise is preceded as a preface by the 174th letter of Augustine and consists of an excerpt from his later work "Return to the Written" (Retractiones). It is addressed to philosophers, theologians and all readers interested in the legacy of world classical thought.