U.S. EPA's Chemical Emergency Preparedness and Prevention Office (CEPPO) provides leadership, advocacy, and assistance to: prevent and prepare for hazardous material (HazMat) emergencies; respond to environmental crises; and inform the public about chemical hazards in their community. To protect human health and the environment, CEPPO develops, implements, and coordinates regulatory and non-regulatory programs. The Office carries out this work in partnership with U.S. EPA Regional Offices, domestic and international organizations in the public and private sectors, and the general public. The purpose of the Semiannual Report on United States-Mexico Border Contingency Planning Activities is to consolidate information on United States-Mexico border joint response and contingency planning from U.S. EPA Regions, border states, and Sister Cities in order to promote the exchange of information and coordination among these groups. The types of U.S.-only and binational activities presented in this report include efforts such as developing Sister City plans, response exercises, training courses, and responses to actual hazardous material and environmental incidents.