As a humanitarian medical organization, Médecins Sans Frontières (MSF) intervenes in places around the world affected by conflict and crisis. Although we are guided by humanitarian principles, our medical teams are often confronted with complicated dilemmas. In a chapter from a new book called Humanitarian Action and Ethics (Zed Books), current and former MSF field workers consider some of the ethical challenges that form an inevitable part of MSF’s medical humanitarian action, and how the organization can better enable our staff and front-line field workers to address them.