This chapter discusses a preventive programme aimed at improving mental health by improving social networks. The programme was carried out in a working-class/middle-class neighbourhood with mainly high-rise houses on the outskirts of Oslo, Norway. It describes an intervention project designed on the basis of the epidemiological study. The project prevents the development of mental disorder by influencing the social network in a positive way, i.e. by social network stimulation. In order to demonstrate the preventive effect of social network stimulation on mental health, one had to select a population group in which the high risk of mental disorder was associated with poor social networks, and expose this group to the programme. Poor quality of life was also included among the criteria because this variable is closely related to mental disorder, especially anxiety and depression, and probably acts as an intervening factor between life problems and mental health.