In recent Trinitarian theology, speaking about God as ‘communio’ has seen a remarkable growth in popularity. The concept of ‘communio’ however, is used in different discussions and with different meanings. In this article three discussions are analyzed. the first concerns the form of Trinitarian theology. I argue that communio should be reserved for ‘the immanent Trinity’. It has a function to clarify speech about God’s working in the creation, rather than describe that working. The second discussion concerns a central and (...) problematic concept in Trinitarian theology, the concept of ‘person’. Based on an interpretation of Thomas Aquinas’s definition of divine person as negative theology, speech about ‘persons in communion’ could help to keep in mind that speaking about persons in God is a negative-theological way of speaking. The third discussion concerns the relation with other parts of systematic theology . From that discussion, it becomes clear that ‘communio’ can be used analogically, as it does not presuppose limitations and it allows gradations. As analogical speech, speaking about God as communio escapes the danger of ideology. Thus, the word communio can rightly and properly be used to say something about God: God is communio. When it is used for creaturely communities as well, it is used in a derivative sense. Because we only know the contents of communio in this derivative way, the meaning of the word remains ‘open’ towards God when we use it to say something about God. A certain negativity remains in our speaking about God as communio. That does not mean that it is irrelevant for speaking about human communities. The concept is a warning that an absolutist priority of ‘unity’ cannot be supported by Christian faith in a God who is a communio of Father, Son and Holy Spirit. This is even more true for the way we live together in the church, sacrament of God’s communio. (shrink)