Downsizing has been an important dimension of organisational restructuring across most OECD economies during the 1990s. Most research has focused on downsizing as an independent variable. Little research has examined downsizing as a dependent variable and even less has focused on the downsizing of occupational groups within organisations. This thesis focuses on the prevalence and causes of intensive occupational downsizing among professionals. Following a critique and development of a new measure of intensive occupational downing, two theoretical perspectives are examined. The first is an economic `costs' perspective that centres on key characteristics of firms and their environments. The second theoretical perspective comprises the new institutional approach that emphasises the legitimacy and diffusion of downsizing as a managerial fad or fashion. The thesis attempts to assess the explanatory weight of the two theoretical perspectives in relation to the decade of downsizing trends in Australia from 1990. The research undertaken has uniquely developed an original longitudinal dataset of over 4000 organisations. For each organisation, ten years of specific structural information is recorded. This thesis represents an empirical examination of the causes of organisational downsizing using a large longitudinal datasetThe results indicate that intensive occupational downsizing impacts on all occupational groups, consistent with international research. Moreover, the results indicate that conventional measures of downsizing have underestimated its prevalence, due primarily to limitations in its measurement. Focusing on professionals, the substantive results indicate that both economic and institutional factors play a role in causing downsizing among the firms examined. However, economic factors play a more significant role in the analysis