Classical Christian orthodoxy insists that God is Triune: there is only one God, but there are three divine Persons - Father, Son, and Holy Spirit - who are somehow of one substance with one another. But what does this doctrine mean? How can we coherently believe that there is only one God if we also believe that there are three divine Persons? This problem, sometimes called the 'threeness-oneness problem' or the 'logical problem of the Trinity', is the focus of this interdisciplinary volume. includes a selection of the most important recent philosophical work on this topic, accompanied with a variety of compelling new essays by philosophers and theologians to further the discussion. The book is divided into four parts, the first three dealing in turn with the three most prominent models for understanding the relations between the Persons of the Trinity: Social Trinitarianism, Latin Trinitarianism, and Relative Trinitarianism. Each section includes essays by both proponents and critics of the relevant model. The volume concludes with a section containing essays by theologians reflecting on the current state of the debate.