Reflective practice is a prerequisite for One Health development.

One Health is being promoted as a transformative approach in health, conservation, and environmental sustainability. The polycrisis of climate change, pandemics, food insecurity, biodiversity loss, pollution and inequity is creating an urgency to evolve the epistemology and methods of One Health. However, the amount of effort placed into critical and systematic reflection on One Health is outweighed by advocacy for its use, or for expanding its scope of practice. This paper advocates for reflective One Health practice to foster new ways of knowing and doing that are helpful in the face of a rapidly narrowing window of opportunity to preserve the social and environmental factors that secure health and resilience for all species and generations. We propose six areas for reflection; (1) how to moderate conformity so that One Health does not become its own silo; (2) finding the moral purpose of One Health to align actions with desired outcomes; (3) coping with the problem of too many interacting problems; (4) the strategic trajectory of growth to accelerate action on root causes and ensure One Health is future-ready; (5) how to identify priorities across a vast array of problems, values, and needs and (6) how to know if we are making the world healthier and safer and for whom. Reflective practice requires investment in ongoing conversation to guard against over-confidence that we have captured the "one right way" to meet changing expectations and circumstances in a fair and effective way. Our intention is to stimulate thinking and discussion within the One Health community to ensure that "doing is shaped by knowing". We hope One Health will continue to be an emergent and highly variable set of ever more effective practices that constantly changes in response to the complex, interconnected and changing problems facing the health of people, animals, and the environment.