Why are there so many behaviour problems in children these days? Do they reflect falling values and standards in society and a breakdown in authority and discipline at home and in school? Are they the hallmarks of increasing deprivation and maladjustment, the outward signs of unfulfilled emotional needs, of conflict between the demands of natural egoism and the conditions of the environment? These questions have been the subject of a number of clinical, epidemiological and statistical studies. Some of these have made use of questionnaires and inventories for the purpose of identifying deviant behaviour and for discriminating between different kinds of behaviour and emotional disorders. Such questionnaires alone, as Tizard (1974) has pointed out, do not always produce valid indices but they are useful as screening devices and in providing descriptions of a wide range of child behaviour.