We conduct a systematic study of the sacraments in general, from both a dogmatic and liturgical viewpoint. Sacraments are studied as acts of communication between God and humans. We start with an anthropological basis: theories of human communication, phenomenology of religion; then move on to the communication God makes of Himself in Revelation: creation, the Old Testament, and the New Testament. This is followed by a historical summary of theological reflection on the sacrament: in patristics, scholasticism, the Reformation and the Council of Trent, the post-Tridentine era, and the present. After a synthetic recapitulation that highlights the centrality of Christ as the fundamental event of God’s communication to man, we proceed to the systematic study of the sacrament: definition, institution, efficacy, the rite, the permanent dimension, grace, and sacramental life, sacramentals.