The history of the Congress has been told. It remains to set forth the principles which controlled the work of the Congress week, and thus scientifically to introduce the scholarly undertaking, the results of which are to speak for themselves in the eight volumes of this publication. Yet in a certain way this scientific introduction has once more to use the language of history. It does not deal with the external development of the Congress, and the story which it has to tell is thus not one of dates and names and events. But the principles which shaped the whole undertaking have themselves a claim to historical treatment; they do not lie before us simply as the subject for a logical disputation or as a plea for a future work. That was the situation of three years ago. At that time various ideas and opposing principles entered into the arena of discussion; but now, since the work is completed, the question can be only of what principles, right or wrong, have really determined the programme. We have thus to interpret that state of mind out of which the purposes and the scientific arrangement of the Congress resulted; and no after-thought of to-day would be a desirable addition. Whatever possible improvements of the plan may suggest themselves in the retrospect can be given only a closing word. It was certainly easy to learn from experience, but first the experience had to be passed through. We have here to interpret the view from that standpoint from which the experience of the Congress was still a matter of the future, and of an uncertain future indeed, full of doubts and fears, and yet full of hopes and possibilities.