The aim of this thesis was to examine the affective and cognitive disturbance associated with weight-loss dieting. We were particularly interested in how mood might interact with dietary restraint to produce cognitive deficit. Initially dieting was investigated in a community sample of overweight dieters. Affect was assessed by self-reported feelings of positive and negative mood (PANAS) and general psychological well-being (Ryff s PWB). Cognitive performance was assessed using a battery of computer administered tasks that measured speed to respond to a target stimulus; immediate memory recall; working memory capacity; vigilance (Bakan task); attentional distraction for food related stimuli (Stroop task); and, preference for food and body-shape related stimuli (Implicit Association Test). In replication of previous studies (e. g. Green, Rogers, Elliman, & Gatenby, 1994), dieting was found to be related to cognitive deficit. The same dieters were also found to be more neurotic and to have greater levels of affective disturbance compared to non-dieters. Contrary to expectation, restraint per se could not account for the dieter-non-dieter differences found. Further, differences in cognitive performance could not be explained as directly due to dieter-non-dieter differences in BMI, hunger, preoccupation, attentional bias or mood. Rather, it was the tendency to eat when emotional which best identified those dieters most vulnerable to cognitive and affective disturbance. Further investigation revealed that under conditions of high negative mood, tendency towards emotional eating was associated with an increase in preference for food related stimuli, and a decrease in attentional capacity. Accordingly, it was proposed that under dieting conditions, where opportunity for affective disturbance is increased, cognitive deficit is most likely to occur in the high emotional eater because they are highly sensitive to affective disturbance, and for them such disturbance results in preferential allocation of attentional resources to food and eating related cognitions. Further research is needed to fully examine the psychological profile of the individual with high tendency towards emotional eating. This issue is of particular importance given the additional finding that the tendency to consume when emotional is not context-bound but can also be observed in other behavioural domains, such as "emotional spending" on other consumer goods.