Francisco de Vitoria, who was interested in all questions concerning human life, found in theology the key to giving answers whose validity has not declined over time. This feature, clearly marked in the ›Relectiones‹, also holds for ›De actibus humanis‹. This hitherto unpublished work is a commentary on the nature of human behavior, which mainly focuses on morality as the ontological reality underlying human acts, disposed as they are (or not) towards the ultimate end. The commentary, in spite of being academic, stands out due to its liveliness and practical sense, as well as its unaffected, down-to-earth style. This very first edition of the ›De actibus humanis‹ is published together with an extensive introductory study and a Spanish translation.