In this chapter we have emphasized that it is of central importance when planning mental health service for populations, to do so on the basis of (i) the occurrence of mental disorders in that particular population, (ii) the impairments caused by these disorders that require interventions, (iii) the nature and level of needs among these people, (iv) identifying from among these needs those which are unmet, and then (v) prioritizing new service development on the basis of these unmet needs, including a range of social supports and services (such as housing or employment opportunities, outside the mental health system), the requirements for enhanced physical/general health care, as well as improvements in the provision of specific mental health services. For all of these sectors there is an increasingly clear call from service user/consumer groups for involvement in these priority-setting planning exercises. At the level of individuals with mental illness, there is a similar trend to increasingly involve service users/consumers in assessing needs, with emerging evidence that this produces a more comprehensive basis for care planning. Indeed in the last decade there has been an important conceptual shift away from the view that professionals defined ‘needs’ while consumers stated ‘demands’, to a better appreciation of the many advantages to be gained from identifying, as far as possible, unmet needs in a joint and consensual way as a basis for action.