Prior to the al Qaeda terrorist attacks on the United States on September 11, 2001, for more than two decades the United States had considered Iran the world's leading country in sponsoring international terrorism. Iranian leaders persistently denied the American accusations, contending that their country has been a victim, not a sponsor, of international terrorism. After September 11, the two nations found themselves on the same side in the war against al Qaeda and the Taliban regime in Afghanistan. As a fundamentalist Sunni movement, the Taliban considered Shi'ia Iran to be an affront to Islam and a mortal enemy. In return, Iran, along with Russia, provided weapons and training to the anti-Taliban Northern Alliance. The American decision to eliminate al Qaeda and the Taliban in the aftermath of the September 11 terrorist attacks served major Iranian strategic and economic goals. Iran's cooperation with the United States included offering to conduct search-and-rescue missions for downed U.S. pilots in Afghanistan, providing a port for shipping American wheat into Afghanistan, playing a key role in forming a government in Kabul led by Hami Karzai, and promising substantial foreign aid to help rebuild Afghanistan. The crux of cooperation between Washington and Tehran was shared antipathy for the Taliban. The two sides share neither identical goals nor similar strategies in Afghanistan and the broader central Asia. By late 2001 signs of growing differences between Washington and Tehran over the conduct of the war on terrorism had resurfaced. After examining this brief period of cooperation between the United States and Iran in the war on al Qaeda and the Taliban, this article analyzes the failed attempt of Iran to smuggle weapons to the Palestinian Authority (the so-called Karine-A affair), the designation of Iran by Washington as part of the global axis of evil, and the Enhanced Border Security and Visa Entry Reform Act of 2002. Despite the strong disagreement on how to define and fight terrorism, this article argues that Iranian and American interests are not mutually exclusive, and there are certain areas where the two countries can cooperate. Specifically, the article suggests how Washington and Tehran can cooperate in policies toward the Palestine-Israel conflict and Iraq. 33 notes