Food and eating may have strong effects on mood. Although many of the ideas put forward by popular writers on this subject have lacked scientific credibility, more rigorous research has begun to identify some important relationships between food and mood. These relationships can be complex, and may be modified by individual and contextual factors. Where they exist, effects of food on mood can be expected to feed back to influence food choice on subsequent occasions. A challenge of future research is to identify the mechanisms which mediate the sensory, nutritional, and pharmacological actions of foods and food constituents on mood.