Physical inactivity is associated with a number of diseases, cardiovascular and respiratory diseases, type-2-diabetes, cancer, and osteoporosis. Worldwide, 17% of the population is estimated to be physically inactive and 40% are estimated to be insufficiently active. In Norway 20% of the population are estimated to be physically active at the recommended level. It might thus be possible to enhance health by increasing the level of physical activity in the population. In March 2009, the Norwegian Health Directorate commissioned the National Knowledge Centre for the Health Services to conduct a review of systematic reviews concerning effects of interventions outside the health services to increase physical activity among adults. The commission is part of the Health Directorate’s contribution to a national strategy for increased physical activity in the population. We included nine systematic reviews of high methodological quality. We conclude, based on our summary of the results and the outcome of our appraisal of the quality of the evidence: Individual-based interventions: Social support and remote support (Internet and telephone) probably increase physical activity levels in the short term. . Advice, exercise and educational materials may increase physical activity levels slightly in the short and long term (> 12 months). . Computer-tailored support, brief advice, pedometers, and programmes promoting active travel may increase physical activity levels slightly in the short term. . We judged the quality of the documentation to be very low for interventions tailored to specific populations, for group-based education and exercise, and for initiatives to promote car sharing in neighbourhoods. We cannot draw conclusions about effects of these interventions. . We lack good documentation about work-place interventions. Population-based interventions: Local point-of-decision-prompts to use the stairs placed by elevators and escalators, campaigns in the community, and enhanced access to places for physical activity combined with informational outreach activities may possibly contribute to a small increase physical actcivity levels. . We judged the quality of the evidence to be very low for campaigns in the media, for campaigns to promote walking and cycling to work, and for community-scale and street-scale urban design and land use policies, meaning that we cannot draw conclusions about effects of these interventions. . We lack information about transportation and travel policies and practices, and interventions implemented through sporting organisations for increasing participation in sports. . We judge the conclusions to be valid for adults in general but not necessarily for groups in the population who are thought to, on average, have a lower level of physical activity and worse health, . the elderly, immigrants from non-Western countries, and physically disabled people.