This paper examines the disciplinary influence and the extent of multidisciplinary doctoral research in tourism in the United States, Canada, Australia and New Zealand. Dissertation databases were mined to identify 1,888 tourism-focussed doctoral theses completed between 1951 and 2010. Abstracts were analysed to determine disciplinary influences, differences between countries, and changes over time. The growth in tourism-focussed doctoral research has been exponential. Overall, psychology, environmental studies and anthropology have informed the greatest number of doctoral dissertations. The influence of some disciplines has declined proportionately over time, most notably economics. The dominance of single disciplinary based research suggests the need for initiatives to foster multidisciplinary research.