Since the Islamic Revolution in 1979, Iran has been one of the world's most active sponsors of terrorism. Tehran has armed, trained, inspired, organized, and otherwise supported dozens of violent groups over the years. Iran has backed not only groups in its Persian Gulf neighborhood, but also terrorists in Lebanon, Israel, Bosnia, the Philippines, and elsewhere. This support remains strong even today. Almost twenty-five years after the revolution, the US State Department still labels Iran “the most active state sponsor of terrorism.”

Of the many terrorist groups that Iran has sponsored, none is more important to Tehran than the Lebanese Hizballah. Their close relationship is perhaps the strongest and most effective relationship between a state sponsor and a terrorist group in history. Iran helped found, organize, and train Hizballah, eventually creating a strong and relatively independent terrorist group. In exchange, Hizballah has served Iran loyally, striking Iran's various foreign enemies, helping assassinate Iranian dissidents, and otherwise advancing the interests of the Islamic Republic.

Iran initially supported Hizballah to spread its Islamic revolution but, over time, strategic reasons have also come to the fore. These changes have occurred largely due to a decline in revolutionary fervor in Iran, Hizballah's gradual accommodation to Lebanon's political and strategic realities, and Tehran's realization that a failure to use Hizballah discreetly can be quite costly. The impact of Iranian support was profound. Hizballah over time became the strongest militia in Lebanon and one of the world's premier terrorist organizations.