Primary prevention aims to reduce the incidence of a disease. The articles in this volume of Schizophrenia Bulletin will focus on primary prevention. Interventions related to primary prevention can be delivered to the general population or to different target populations.19,20 A preventive intervention aimed at the general population regardless of risk status is termed “universal prevention.” Rose18 emphasized that such population-based interventions are best suited to risks that are distributed throughout the population, albeit not in equal measure. Those at high risk of disease, seemingly an obvious target for preventative action, may, in fact, be relatively rare. Those at medium risk may be more common and thus may account for a much higher proportion of those who eventually develop the disease. Rose18 introduced the concept of the “prevention paradox”—a preventive measure may deliver benefits to the community at large but may offer little to the majority of that community who are, themselves, at low risk. Indeed, population-based (universal) intervention may mean that such low-risk individuals have to give up something (eg, wear a seat belt, eat fortified food, have vaccinations) in order to reduce the community burden—hence the paradox.