Providing aid to people in crisis is never enough—it must meet their most urgent needs and be grounded in sound science. Aid agencies have a responsibility to determine the effectiveness of their response and use evidence-based approaches. This article describes the history of Médecins Sans Frontières’ move towards professionalization in response to the challenges it faced in the field and explores the sometimes unintended organizational consequences that accompanied this move. The article highlights key questions linked to professionalization and accreditation of aid agencies that are part of an ongoing debate in the humanitarian sector through a review of the practical experience of one organization and outlining some of the pitfalls of the approaches currently proposed. Responding professionally to increasingly complex needs while retaining the humanitarian spirit that responds to unacceptable human suffering is a major challenge facing aid agencies. This challenge will not be addressed simply by introducing more regulation, as proposed recently by schemes to credential aid agencies, but requires old-fashioned idealists willing to challenge the status quo while providing professional interventions appropriate to the context.