This chapter examines several behavioural regularities explaining health behaviours that provide alternative behavioural explanations of actual preventative choices (e.g., smoking, weight loss, exercise, safe sex). The chapter discusses the roles of taxes and information and how social incentives and designs that incorporate social and monetary incentives keeping in mind biases such as loss aversion can help change behaviour. The chapter describes biases related to prevention failures such as optimism, present and status quo biases and includes examples of prevention failures in health-related behaviours.