Each state's physical environment, economy, and politics demands a unique approach to environmental enforcement. In some states, industry works closely with regulators to construct rules that protect state economic interests. In other states, regulators are more at odds with industry, arguing that there can be no cost placed on access to clean air and water. While we have long-considered powerful legislatures and governors the pilots of environmental enforcement behavior in the states, focusing on elected officials ignores the pivotal role environmental agencies and their employees play in determining the overall direction of environmental policy through day-to-day enforcement decisions—decisions to negotiate with industry or to stand firm. In Environmental Agencies in the United States, the author looks closely at the mandates assigned to environmental agencies and how those mandates mold agency understanding of the purpose of environmental enforcement. In arguing the importance of agency structure, organizational norms, and the mediating effects of state politics, the author crafts a more nuanced explanation of the environmental policy variation that shapes the health of all Americans.