The Apostle John teaches that God is love. The Lemma Ioanneum (1Jn 4:8) is one of the most important topics in the history of Christian theology, as it offers a precious insight into the depths of the Trinitarian mystery. In this work, which is both original and faithful to the Magisterium of the Catholic Church, the author develops a theological system that springs from an ontological-relational understanding of the Johannine passage. Central to this book is the three-fold demonstration that in God Love and Being are one and the same thing. The affirmation that God is Love from the depths of His nature to the heights of His triune character leads to a new understanding of our own reality. The concluding chapter on marriage constitutes an example of how an agapic Trinitarian theology can lead to a deeper comprehension of all other theological disciplines. Eric E. Puosi was born in Viareggio, a small town along the north shore of Tuscany. He studied in American schools and received his High School Diploma in New Jersey. In 1993 he began his theological studies at Pontifical universities in Rome and Tuscany. During this time he also worked as a journalist for a national newspaper leading to his candidature for the Tuscan Parliament. In 2001 he left his journalistic and political career committing himself to the study of theology at the University of Aberdeen (Scotland). By 2006 he received his Doctorate from the same institution. He is the author of various theological articles and co-editor with Francesca Murphy and Chris Asprey of the book Ecumenism Today.