There is currently no solid basis for assuming that a particular intervention or package of interventions will work. Effective interventions to increase preventive activities in primary care exist, but there is considerable variation in the level of change achieved, with effect sizes usually small or moderate. Tailoring interventions to address specific barriers to change in a particular setting is probably important. Multifaceted interventions may be more effective than single interventions, because more barriers to change can be addressed. Future research should analyse barriers to change and interventions to implement preventive services in more detail, to clarify how interventions relate to specific barriers. Since more complex interventions are likely to be more effective but also more costly, economic evaluations should also be included.