Charles Weijer is Professor of Medicine, Epidemiology & Biostatistics, and Philosophy at Western University in London, Canada. He is a leading expert in the ethics of randomized controlled trials. From 2008 to 2013 Charles co-led a collaboration that produced the first international ethics guidelines for cluster randomized trials. His current work explores ethical issues in pragmatic randomized controlled trials that evaluate health interventions in real-world conditions to better inform patients, health providers and health systems managers. Charles led the writing team for the World Health Organization guidance on “Ethical Considerations for Health Policy and Systems Research,” published in 2019. In 2020, he served on the WHO Working Group for Guidance on Human Challenge Studies in COVID-19. Charles held the Canada Research Chair in Bioethics from 2005 to 2019, and, in 2016, he was elected to the Royal Society of Canada.