In this brief primer on prevention, the authors raise some of the scientific, social, behavioural, political and practical issues that must be addressed to integrate effective preventive initiatives into our health system (which includes public health practice). They begin by reviewing the contributions science has and has not made to inform our prevention efforts. The authors further examine what it is we know about changing human behaviour in health-promoting ways. The article closes with a review of the practical challenges for prevention-oriented policies and programs in the health system and in society as a whole. The authors call for increased emphasis on strategies that encourage the creation of supportive environments. Moreover, they identify that we need to try for fewer, but better-thought-out and more sustained, multi-level health promotion and disease prevention interventions. Community-led interventions that identify, address and change local cultural norms that contribute to these health concerns are especially key. Finally, the authors identify the need for rigorous evaluation to ensure that all effects, good and bad, of preventive interventions are fully captured and addressed.