In recent decades, the focus on environmental issues has grown rapidly, with ozone depletion, loss of biodiversity, air pollution, soil pollution, and water pollution being among the topics of concern. These topics have been discussed and analyzed in international governmental and nongovernmental fora, and this has led to a considerable growth in the number of international agreements and institutions dealing with environmental issues. The evolution of international treaties over the last decades has had a positive impact on the international community’s awareness of environmental issues and has spearheaded environmental improvements, such as reductions in air pollution and protection of the ozone layer. But the rapid growth of international agreements and institutions has also raised questions as to how effective or coherent the international response to environmental problems really is. The evolution of the climate change regime, in particular, demonstrates the institutional and legal constraints to elaborating international environmental agreements, and the challenges that this involves.