The subtle relationship between feeling and thinking, affect and cognition has fascinated philosophers and writers since time immemorial, yet, empirical research on this topic was relatively neglected by psychologists until recently. There have been many claims emphasising the beneficial cognitive and behavioural consequences of positive affect. Many recent works suggest that negative affect may also facilitate optimal performance in many situations, consistent with evolutionary theories suggesting the adaptive signalling function of various affective states. This paper reviews traditional and current psychological theories linking affect to social thinking and behaviour. A variety of empirical studies from our laboratory will also be presented, demonstrating that in many situations, negative affect promotes optimal performance in cognitive and social tasks, including tasks such as memory, social judgements, motivation, and strategic interpersonal behaviours. These results will be interpreted in terms of a dual-process theory that predicts that negative affect promotes a more accommodative, vigilant, and externally focused thinking strategy. The relevance of these findings for recent affect-cognition theories will be discussed, and the practical implications of negative affect promoting improved social thinking and performance in a number of applied fields will be considered.