Besides showing the importance for mental development of the problems connected with family life, modern psychological research has also revealed something of the nature of these problems. It is true that of the results obtained in this field there are as yet few, if any, which can be regarded as definitely settled; many, no doubt, will, in the light of future work, be seen to require more or less extensive revision, qualification or addition; some perhaps may have to be rejected altogether. Nevertheless it would appear that, as a consequence of the work already done, certain main principles at least have emerged so clearly as to justify, if not indeed to demand, the serious attention of all those who, at this critical period of human history, have to deal directly or indirectly with questions affecting family life in one or more of its numerous aspects. The sociologist, the moralist, the spiritual adviser, the teacher, the family physician and the parent are all intimately concerned with such questions; and it is primarily with the needs of such as these in view that the present brief exposition of the subject has been undertaken. After what has been already said, it is perhaps unnecessary to offer any further warning against accepting all the results of psychological investigation which are here set forth as claiming equal validity or as being equally capable of generalisation or application on a large scale. No dogmatic enunciation of facts or principles is here attempted or desired, even where, owing to the endeavour to avoid entering upon the discussion of matters too intricate or controversial to fall within the scope of our present treatment, the statements may possibly appear somewhat dogmatic in form. Our aim is rather to produce a more widespread realisation of the immense and far-reaching significance of the psychological problems connected with family life; to indicate some of the ways in which psychological knowledge has thrown light upon the solutions of these problems; and perhaps, by these means, to be of some assistance to that very large class of persons who, at one time or another during their lives, find themselves compelled to deal with such problems--whether as entering into their own lives, as affecting others for whom they are responsible, or as forming part of larger questions, social, religious, medical or pedagogic, in which they have an interest. To those who have once realised the complexity, the obscurity, and above all the tremendous intensity of the psychic factors entering into these problems, there can be little doubt that in so far as Psychology is able to afford some reasonably sure guidance as to their solution, it will have achieved one of the most successful and valuable of all applications of science to social and ethical phenomena. The time for such application on a large scale has not yet come. But the progress that has been already made would seem to indicate that the expectation of some