Gillian Reeves is Professor of Statistical Epidemiology and Director of the Cancer Epidemiology Unit in the Nuffield Department of Population Health at the University of Oxford. She trained originally as a statistician and completed a PhD in statistics at Imperial College before joining the Cancer Epidemiology Unit in Oxford as a medical statistician. In the early 1990s, she was involved in setting up the Collaborative Group on Hormonal Factors in Breast Cancer, a large international collaboration of over 100 epidemiological studies, which has generated key findings on the role of oral contraceptives and HRT in breast cancer incidence, and influenced clinical practice. She is a PI for the Million Women Study, a very large UK cohort study of women’s health, which provides the basis for much of her epidemiological research. Her main research interests are the prevention and early detection of breast and other cancers.