The unity of the church is one of the fundamental goals of the ecumenical movement. But what is unity precisely? Ecumenical documents often refer to the concept of "visible unity", but this is not as firmly defined as it might appear at first sight. This study of the Ecumenical Study Committee of VELKD and GNC/LWF would like to contribute to the clarification, whether and in what sense "visible unity" is a necessary or at least sensible ecclesiological goal for Lutheran theology. This clarification is at the same time a helpful resource for future ecumenical conversations.