Unsafe abortion is a significant yet preventable cause of maternal mortality and morbidity in developing countries. This report contains the papers submitted to an interdisciplinary consultation convened by WHO to assess the problem of unsafe abortion globally and to identify a research agenda aimed at reducing unintended pregnancy, unsafe abortion, and the resultant burden on women, their families, and public health systems. Experts at the consultation reviewed the available evidence on unsafe abortion, examined the factors that perpetuate the problem, and identified both opportunities for preventing unsafe abortion and constraints on prevention. Participants addressed the theoretical and medical issues relating to research on unsafe abortion and outlined regional priorities for the prevention of unsafe abortion. Both long-standing and emerging issues relating to research on unsafe abortion were discussed.