According to the U.S. Air Force Posture Statement 2008, at any given moment the USAF has more than 26,000 Airmen deployed to fight the global war on terrorism. Of those deployed, over 6,200 directly support the land component commander by filling in lieu of taskings with the U.S. Army. While deployed to the Central Command area of responsibility, our Airmen face a growing tactical threat from increasingly hostile and deadly attacks from Iraqi Shia militia groups, such as the Mahdi Army and the Badr Brigade. These groups are directly and indirectly supported by Iran. Iran's support to the Shia militias in Iraq has both tactical-level and strategic-level implications for U.S. security policy. This article focuses on the security challenge posed by Iranian support for terrorism, specifically its support of Iraqi Shia militias. In doing so, it poses the following research questions: What causes the Iranian government to provide material and economic support for Shia militias in Iraq?; and What is the most appropriate U.S. security policy response? To answer these questions, the article is divided into three sections, each centered on a sub-question or analytical area: (1) What explains the variation in the degree and strength of Iranian (and presumably Iranian Revolutionary Guard Corps) support for armed groups like the Badr Brigade and the Mahdi Army?; (2) In what ways, or through which vehicles, would Iran be most likely to lend its support to Iraqi Shia militia groups?; and (3) Regarding Iran, what is the most appropriate U.S. security policy response? The author addresses the issue in earnest and provides the reader with increased knowledge and understanding of this complex relationship in addition to providing sound policy prescriptions for dealing with this growing security threat.