Large accounting firms have been structuring their audit divisions along industry lines for some years. Industry specialisation is seen as a means of differentiation between otherwise similar accounting firms. At the individual level industry specialists are identified as being so designated within their firm. They spend a substantial amount of their time auditing clients in that industry. The purpose of this study is to determine what industry specialist auditors do that is different and similar when working on industry-based tasks, one of which they specialise in. Behavioural decision theory is used to investigate the differences and similarities in the decision-making processes of industry specialist and other auditors. It is known that industry specialists perform better on tasks set in their industry. The purpose of this study is to learn why. To that end, the pre-information search, information search and decision processing phases of the decision-making process are examined. It is expected that industry specialists are more efficient and effective at each stage of the decision-making process when completing a case set in the industry they specialise in. Two controlled experiments were conducted in the offices of each of the Big 4 international accounting firms. Participants included manufacturing and superannuation industry specialists from each firm. Each participant was invited to take part in both experiments, which were conducted consecutively via the internet. The first experiment comprised two cases, one set in each industry setting (manufacturing and superannuation). Participants completed both cases. The purpose of the first experiment was to conduct a within-subject examination unveiling similarities and differences between industry specialists and other auditors during the pre-information search, information search and decision processing phases of the decision-making process. Their performance on each case was also monitored and measured. Significant results were found for information search and performance. Moderate results were found for one proxy each of the pre-information search and the decision processing phases. The relationship between efficiency at each stage of the decision-making process and performance was also measured. A significant relationship was found for the pre-information search and decision processing phases. The second experiment comprised two strategic business risk tasks set in each industry setting (manufacturing and superannuation). Participants completed both sets of tasks. The purpose of the second experiment was to examine effectiveness during the pre-information search (listing key strategic business risks), information search (listing key inputs) and decision processing (listing key processes) phases of the decision-making process and their ability to identify and list key outputs (accounts and assertions) for an identified risk (technological change for the manufacturing industry task and solvency due to insufficient funding for the superannuation industry task) within each industry setting. The results were very significant overall. Industry specialist auditors were able list more key strategic business risks, inputs, processes and outputs when the task was set in the industry in which they specialise. The relationship between effectiveness at each stage of the decision-making process and performance was also measured. A significant relationship was found between effectiveness in listing key inputs and effectiveness in listing key outputs (accounts).