This lecture delves into international climate policy, focusing on the concept of mitigation as a public good. It covers the economic aspects of abatement measures, the cost of mitigation, and the theory of market failure. The discussion includes the characteristics of GHG abatement as a public good, the challenges of free riding, and strategies to solve the Prisoner's Dilemma in climate agreements through game theory insights and self-enforcing designs. The instructor explores the importance of considering everyone's benefit in achieving socially optimal solutions and the role of norms and appeals in global climate governance.