This paper investigates the concept of missio Dei at Willingen and beyond, and identifies its most remarkable feature which regards God as the initiator and subject of mission, thereby redefining missio ecclesiae with three striking characteristics: first, all places of the world including both the immediate neighborhood and the uttermost parts of the earths; second, all spheres of life such as society, politics, economy and culture; and finally, all events of the time such as catastrophes in the history. In so doing, this paper clearly discovers that missio Dei is here approached primarily in a differentiation from or a sharp contrast to missio ecclesiae from the start, and that, for that reason, the concept of missio Dei at Willingen and beyond has not been fully trinitarian, though it often mentions the triune God. And it also discovers that it goes further either toward an emphasis on culture on the one hand, or toward that on the world on the other hand. Such being the case, this paper suggests that it is necessary to consider the implications of the doctrine of the Trinity for mission more fully to reconfigure the concept of missio Dei . Due to some limits, this paper does not deal with this issue full-fledgedly, but intends to suggest a couple of guidelines for doing so. First, we need to approach missio Dei quite differently, that is, primarily not in relation to missio ecclesiae but in relation to processio Dei , that is, the procession of the triune God. Second, noting that, since the early church, missio Dei has been understood primarily in relation to processio Dei , we need to keep in mind that we could not discuss missio more fully without dealing with processio , and vice versa . If we have these two guidelines in mind, the concept of missio Dei would be much more abundant and fruitful. Further studies on some particular implications of the doctrine of the Trinity for mission need to be done in missiology and also theology in general in the near future.