Obesity is a serious public health problem that has important social, economic and health consequences. The prevalence of obesity is rising rapidly throughout the world in both rich and poor countries, and it affects all sections of society. There are several important reasons for addressing the prevention of obesity, rather than its treatment or management. The prevention of weight gain (or the reversal of small gains) and the maintenance of a healthy weight are likely to be easier, less expensive and potentially more effective than the treatment of obesity after it has fully developed. A structured planning framework for the identification of potential interventions for the promotion of healthy weight and the prevention of weight gain is clearly required. However, detailed reviews of the scientific literature have revealed that the body of research is too small to provide firm guidance on consistently-effective interventions for adults or children. Ultimately, a broader approach to evidence of effectiveness needs to be adopted. The present paper proposes a structured planning approach that utilises the portfolio model and allows the selection of interventions to be based on the best available evidence, while not excluding untried but promising strategies.