To assist the Department of Homeland security in its efforts to safeguard the Nation’s people, infrastructure, and economy from terrorist use of improvised explosive devices (IEDs), this report prioritizes precursor chemicals that can be used to make homemade explosives and analyzes the movement of those chemicals through United States commercial supply chains and identifies potential vulnerabilities. It also examines current United States and international regulation of the chemicals, and compares the economic, security, and other tradeoffs among potential control strategies.