The enactment of the Montreal Protocol in 1987 is hailed as a success for international cooperation in general, and environmental policy in particular. In this talk, Dr. Peter Thacher, a retired UN diplomat, explains the circumstances surrounding the identification of the ozone hole problem and the subsequent agreement to curb CFC emissions, the leading contributor to ozone depletion. Dr. Thacher argues that there are lessons to be learned from this case-study that can be applied to future cases of cooperation on environmental issues.