John Guillebaud is Emeritus Professor of Family Planning and Reproductive Health, University College London. Until 2003 he was the Medical Director of the Margaret Pyke Centre for Family Planning and is currently a vasectomy surgeon at the Churchill Hospital, Oxford. He acts as a consultant to the World Health Organization (WHO) and other national and international bodies in the reproductive health field. He originated the Environment Time Capsule Project at www.ecotimecapsule.com, is Trustee of TASKwh (Towards African Solutions through Knowledge for Women's Health), Co-Chair of www.populationandsustainability.org, and Chair of Planet 21 (www.peopleandplanet.net ). Dr Anne MacGregor works in sexual and reproductive healthcare at St Bartholomew's Hospital and is an Instructing Doctor and CRQ Vice Convener for the Faculty of Sexual and Reproductive Healthcare of the Royal College of Obstetricians and Gynaecologists. She is also Clinical Research Director at the City of London Migraine Clinic, an independent medical charity, and Honorary Senior Clinical Lecturer at the Research Centre for Neuroscience within the Institute of Cell and Molecular Science, Queen Mary's School of Medicine and Dentistry, London.