The special branch of social anthropology which deals with peoples whose culture is undergoing rapid change as the result of contact with more highly developed societies is of interest from a number of different points of view. On the one hand there is the purely theoretic approach, which is concerned to discover rules governing this process—to find reasons for the assimilation of some elements of the alien culture and the rejection of others, or explanations of the fact that the dominant civilization has sometimes succeeded in imposing changes in social organization which analysis shows to be patently disadvantageous, while in other directions it may be powerless; perhaps to trace the basic human motives which come sharply into prominence when liberated by the breakdown of traditional standards of conduct and values. On the other hand this study has a severely and urgently practical importance. A recent American writer has suggested that in British colonies these problems are only considered relevant in their bearing on the maintenance of the labour supply. Such a view would appear to conflict with the fact that, as far as Africa is concerned, it is mainly in colonies governed under the system of Indirect Rule, where the economic policy is to encourage independent native production, that the study of social anthropology receives official encouragement. Actually it is being more and more clearly recognized by administrators directly concerned in moulding the development of the African peoples that this ‘sacred trust’ cannot be executed until the bases of a sound development are laid down; until it is known in each separate case how far the native social organization has been already rendered obsolete by changed conditions, how far it is capable of readjustment, what are the existing foundations on which the new institutions that the new needs require can be securely built. Experience is constantly bringing home to the man on the spot the need for some more practical criterion of policy than that inherent desirability of everything ‘civilized’, which the facts so plainly contradict.