On May 3-4, 2000, the Environmental Law Institute convened the third United States ? Mexico Workshop on Transboundary Environmental Enforcement. This summary aims to capture the range of ideas and overarching themes of the third workshop, which was divided into three broad topics: (1) moving goods across the border: hazardous wastes and CFCs; (2) pollution with transboundary effects; and (3) liability and use of courts across the border. Each session was introduced by panelists from the U.S. and Mexico who shared their perspectives with the group and stimulated discussion on the topics before them. After many years of formal and informal cooperation in transboundary environmental enforcement, it is clear that the level and effectiveness of coordination is rising. It is also clear that further effort is needed to improve understanding of our respective environmental enforcement institutions and systems; coordinate efforts; increase the quality and quantity of information exchange among government agencies and with the public; and enhance the capacity of citizen enforcers.