Jerilynn C. Prior BA, MD, FRCPC is a Professor of Endocrinology at the University of British Columbia in Vancouver, BC. She studies menstrual cycles and the effects of the cycle’s changing estrogen and progesterone (ovulation) levels on women’s health. She is the founder (2002) and Scientific Director of the Centre for Menstrual Cycle and Ovulation Research (www.CeMCOR.ca--3500-7000 page-views/d. She is also Director of the BC Centre of the Canadian Multicentre Osteoporosis Study (www.camos.org) that studies bone health and incident fracture over almost 20 years in population-based women and men. Dr. Prior is known for innovative research showing:  1) perimenopause is a time of higher and erratic estrogen/lower progesterone levels and paradoxical bone loss (Prior Estrogen’s Storm Season—stories of perimenopause); 2) normally ovulatory cycles are necessary to prevent bone loss—progesterone increases bone formation; and 3) that combined hormonal birth control use is associated with decreased adolescent women’s peak bone mass accrual.