Background: Deficits in the processing of emotional stimuli have long been associated with major depressive disorder (MDD). These emotional biases are believed central to the symptomatology of MDD, with evidence growing that such biases can also be seen during remission. Although such changes are typical of psychiatric morbidity evidence is growing for the impact of ageing on emotional processing as well. Evidence shows that relative to younger adults, older adults demonstrate biases that favour positive information over negative. There is therefore overlap between MDD and normal ageing that has yet to be explored in the literature. Because positive biases are implicated in successful ageing it is important to consider the impact of previous MDD as individuals age. It is this question that is explored in this thesis.Study 1: A behavioural neuropsychological investigation was undertaken comparing older and younger adults with and without a history of MDD on a battery of affective cognitive tasks. Results suggested that the difference between the older adults with and without a history of MDD lay in their ability to disengage from negative information.Study 2: An fMRI investigation was undertaken in a subset of the study 1 sample using neuroimaging paradigms assessing memory encoding and attention for emotional stimuli. Broadly results suggested no influence of previous MDD on the processing of emotional information in the studied domains, with evidence seen in both tasks for the neural basis of the positivity effect of ageing.Study 3: A resting-state fMRI investigation of brain connectivity was undertaken to assess the influence of previous MDD and normal ageing on the communication structure of the brain. Results were largely suggestive of the influence of normal healthy ageing, with limited evidence of the influence of previous MDD or its interaction with ageing.Conclusions: Results were mixed across the investigations. Generally speaking the initial behavioural study was best powered to investigation the questions of interest, suggesting the potential for differential affective processing strategies in later life dependent on previous MDD. The subsequent imaging studies were perhaps less well placed to draw conclusions given limitations in terms of the domains investigated and the sample size. Evidence for the postulate that previous MDD impacts the development of the positivity effect has therefore been demonstrated, but for now remains limited to the behavioural domain.