This thesis is concerned with cognitive biases in depression, with particular focus on attentional and interpretive biases. It reviews cognitive theories of depression, such as those of Beck (1976) and Bower (1981), who predicted that depressed individuals will selectively attend to negative information and will show an enhanced tendency to impose negative interpretations on ambiguous information. In contrast, Williams, Watts, MacLeod, and Mathews (1997) argue that depression is more strongly associated with a bias for negative information in memory, and that depression is not associated with an attentional bias. The methodologies developed for assessing attentional and interpretive bias are described, and research into these biases in depression are reviewed. More recently, attentional bias has been considered in relation to the differing attentional processes of shift, hold and disengagement. It has been suggested that depression may be associated with difficulties in disengaging attention from negative information. Evidence of attentional and interpretive biases in depression is mixed, and further research is required, particularly using clinically depressed samples. The empirical study examined attentional and interpretive biases in clinically depressed participants and non-depressed controls. The study used: (a) an attentional cueing task, (b) a homophone task, and (c) a morphed faces task. It was predicted that an attentional bias for negative information, and a negative interpretive bias for ambiguous information, would be found in clinically depressed participants. Neither of these predictions was supported. While the present study did not detect attentional and interpretive biases in depression, these biases may be found in future research using different methodologies.