The heaviest burden of illness today is related to individual and group behaviour. Numerous other behaviours are also highly relevant to health and disease, both mental and physical, of the individual and those around him (for example violence and suicide). Cigarette-smoking is the single most important environmental factor contributing to early death in the more developed countries. In developing countries, as in developed ones, health and behaviour are indivisible. An important precursor for an expanded research programme is a systematic assessment of the burden of illness that is attributable to psychosocial factors. This chapter presents the editors' comments on the following three topics: the social context of health, the development of children and adolescents, and mental health in general health care. Involving general health services may not be enough: even if they are fully involved, much remains undone, as the experience of developed countries has demonstrated.