In most high-income countries, including Canada, the share of births by Caesarean section (C‑section) has risen over the past decades to far exceed World Health Organization recommendations of the proportion justified on medical grounds (15 percent). Although unnecessary C-sections represent an important cost for health care systems, they are not associated with clear benefits for the mother and the child and can sometimes represent additional risks. Drawing on administrative records of nearly four million births in Canada, as well as macro data from the United States and Australia, the authors provide a comprehensive account of rising C-section rates. The authors explicitly consider the contributions of the main factors brought forward in the policy literature, including changing characteristics of mothers, births, and physicians as well as changing financial incentives for C-section deliveries. These factors account for at most one-half of the increase in C-section rates. The majority of the remaining increase in C-sections over the period 1994–2011 occurred in the early 2000s. The authors suggest that some event or shock in the early 2000s is likely the primary determinant of the recent strong increase in the C-section rate in Canada.