Background: The intake of food and drink can influence brain functions, which in turn may have effects on mental state and performance. Therefore, in principle claims to improve mood or specific aspects of cognitive performance by the consumption of functional foods are possible and indeed are currently found on the market. Aim: The paper reviews existing methodologies, which may be used to substantiate and validate such claims of desirable effects of foods on mental state and performance. Results: Mood, arousal, activation, vigilance, attention, sleep, motivation, effort, perception, memory and intelligence have been identified as relevant aspects of mental state and performance. The basic scientific concepts within this field as well as the methodologies to measure these concepts have been reviewed and described. Conclusions: From this review it is concluded that, in principle, the phenomena in these fields are no different to those in other fields of life science. The scientific methods and protocols described in this report can positively demonstrate the effects of foods on mental state and performance in a scientifically valid way. A claim on mental state and performance like other claims must be based on scientific evidence. This report confirms that methodologies do exist to generate sound scientific evidence in this area. Therefore, claims on the enhancement of specific mental functions can and should be substantiated and validated using the methodologies described in this review.