On February 22, 2010, terrorist Najibullah Zazi pled guilty to conspiring to use weapons of mass destruction, conspiring to commit murder in a foreign country, and providing material support to a foreign terrorist organization. During the run-up to his disrupted plot, Zazi purchased numerous commercial products that he was trained to transform into deadly explosives. Zazi’s attempt to manufacture and use improvised explosives (IEs)—those that can be readily produced from common consumer products or commercial chemicals—was far from an isolated event. Terrorist usage of IEs is on the rise worldwide. To protect the security of the country and ensure their own personal safety, law enforcement officers must have a basic understanding of this evolving threat.