Historically hazardous materials transportation regulations have been enforced by the U.S. Department of Transportation, since they developed the regulations. State and some local police participate in the enforcement. The Research and Special Programs Administration, a separate administration within the Department of Transportation, is responsible for the implementation of hazardous materials regulations. A number of steps are involved in achieving compliance with the hazardous materials transportation regulations. The first stage involves inspection, enforcement, and prevention activities. Another step involves a finding of either a violation or an accident involving the material. The next step consists of either an emergency response to the accident or its investigation depending on the agency's jurisdiction and responsibilities. This leads to mitigation activities during the response, possible citations, or prosecution. The accident is then critiqued and statistics are generated to provide the information necessary for any modification of laws or regulations. In this continuous cycle of activities, agencies interact with one another. This article details procedures and aspects of each step in the cycle and discusses the training required for law enforcement personnel involved.