The status and explanatory role of nutrition knowledge is uncertain in public health nutrition. Much of the uncertainty about this area has been generated by conceptual confusion about the nature of knowledge and behaviours, and, nutrition knowledge and food behaviours in particular. So the paper describes several key concepts in some detail. The main argument is that ‘nutrition knowledge’ is a necessary but not sufficient factor for changes in consumers’ food behaviours. Several classes of food behaviours and their causation are discussed. They are influenced by a number of environmental and intra-individual factors, including motivations. The interplay between motivational factors and information processing is important for nutrition promoters as is the distinction between declarative and procedural knowledge. Consideration of the domains of nutrition knowledge shows that their utility is likely to be related to consumers’ and nutritionists’ particular goals and viewpoints. A brief survey of the recent literature shows that the evidence for the influence of nutrition knowledge on food behaviours is mixed. Nevertheless, recent work suggests that nutrition knowledge may play a small but pivotal role in the adoption of healthier food habits. The implications of this overview for public health nutrition are: (i) We need to pay greater attention to the development of children's and adults’ knowledge frameworks (schema building); (ii) There is a need for a renewed proactive role for the education sector; (iii) We need to take account of consumers’ personal food goals and their acquisition of procedural knowledge which will enable them to attain their goals; (iv) Finally, much more research into the ways people learn and use food-related knowledge is required in the form of experimental interventions and longitudinal studies.