Due to the ageing population, an increasing number of older workers form the labour force. Unfortunately discriminatory practices against older workers are well documented and the antecedents of such discrimination are assumed to be negative attitudes towards older workers. No previous research has investigated implicit attitudes towards older workers or their behavioural consequences. Accordingly, the present research aimed to investigate both implicit and explicit attitudes towards older workers, and their predictive utility in an employment-related context. In addition, attitude malleability and the role it may play in the attitude-behaviour relationship was investigated. This thesis reports findings from 5 studies, a pilot study and 4 main studies. The pilot study determined that the Implicit Association Test (IAT; A.G. Greenwald, D. E. McGhee & J. L. K. Schwartz, 1998) was to be used in the main studies. The 4 main studies investigated implicit attitudes, and the malleability of such attitudes towards older, relative to younger, workers. The malleability of attitudes was investigated with a mental imagery intervention where the experimental group participants were asked to imagine and describe respected and valued older workers in their surroundings. The control group participants were asked to imagine holiday destinations they would like to visit. In general, it was expected that negative implicit and explicit attitudes would be found towards older workers but that such bias could be alleviated with a mental imagery intervention. In all studies, negative implicit attitudes against older workers were found and such attitudes were relatively uninfluenced by the mental imagery manipulation. Three studies included explicit measures of attitudes. Although some variation was found between the studies and the measures used, overall positive attitudes towards older and younger workers were found. The mental imagery manipulation was also found to influence the explicit attitudes to a greater degree than implicit attitudes. The final study investigated the relationship between attitudes and behaviour. Specifically, both implicit and explicit attitudes’ relationships with spontaneous and controlled-type behaviours towards an older and a younger target were examined. Overall, some evidence for youth-bias in the participants’ behaviour was found, as well as evidence for the relationship between explicit attitudes and spontaneous behaviours. Implicit attitudes were largely unrelated to behaviour. In general, the mental imagery intervention did not impact the attitude-behaviour relationship. Implications for older workers are discussed, as well as educational methods for reducing discrimination older workers face in employment.