Human activity over the last century has significantly damaged the Earth’s atmosphere, water, land, and biodiversity. Environmental problems such as stratopsheric ozone depletion (see Chapter 29), acid rain (see Chapter 30), climate change (see Chapter 28), collapse of fish stocks (see Chapter 36), water pollution (see Chapter 34), and deforestation (see Chapter 38) represent challenges from local to global levels. A central focus of this Handbook is explaining and understanding human behavior that has led to environment problems, and the methods and tools to alter this behavior. This chapter focuses on international environmental regimes, which have evolved since the 1970s, as important actors in international environmental politics and as an influential research topic.