December 2002: Satellite photos reveal nuclear sites at program at Natanz and Arak.
February, 2003: IAEA head Mohammed Al Baradei arrives with a team to inspect nuclear sites and plans.
August 2003: Weapons grade uranium is discovered at Natanz.
October, 2003: Iran says it will stop producing enriched uranium and agrees to sign the Additional Protocol, after meeting with French, German and British foreign ministers.
November 2003: The US disagrees with Al Baradei's conclusion that Iran is seeking to build nuclear weapons.
December 2003: Iran signs Additional Protocol.
September 2004: The IAEA orders Iran to stop planning uranium enrichment. US Secretary of State Colin Powell urges UN Security Council sanctions.
November 2004: Iran agrees with the EU to temporarily suspend uranium enrichment, while the status of the nuclear program is being negotiated.
January 2005: Iran allows inspectors into the Parchin plant.
April 2005: Iran indicates that uranium conversion at Isfahan will be resumed.
May 2005: the EU warns that resuming uranium conversation will halt trade and economic negotiations.
August 2005: Under newly elected president Mahmud Ahmadinejad, Iran announces its plan to resume uranium enrichment.
September 2005: Ahmadinejad asserts Iran's right to process nuclear fuels on its own soil and claims Iran seeks nuclear energy for peaceful purposes.
2006: Iran declares that it will no longer cooperate voluntarily with the IAEA. Negotiations between Russia and Iran over whether Russia might process uranium for Iran continue.
March 2006: After repeatedly remarking Iran's unwillingness to be more transparent about its nuclear activities, IAEA head El Baradei says he will forward a report on this issue to the U.N. Security Council. At the end of the month, the Security Council approves a statement requesting Iran to halt nuclear activities.
July 2006: A U.N. resolution demanded that Iran suspend nuclear enrichment and reprocessing by the end of August. Iran ignored the demand.
September 2006: The IAEA contested a House of Representatives report, saying it exaggerated claims of Iran's nuclear preparedness. Iran and the European Union cancel negotiations on uranium enrichment.
October 2006: President Bush signs Freedom Support Act into law, authorizing sanctions against any country that provides support for Iran's nuclear program.
October-November 2006: The IAEA finds evidence that enrichment technology is operable. It also finds traces of materials required for atomic warheads at a nuclear waste facility.
December 2006: The UN Security Council votes unanimously to impose sanctions to halt Iran's ability to acquire nuclear technology or materials, including the demand that enrichment program stop immediately. Iran declares that sanctions will not halt its ability to continue nuclear work.
January 2007: Iran says the U.N. sanctions will not halt its uranium enrichment.
March 2007: UN Security Council imposes second round of sanctions on Iran.
October 2007: United States imposes unilateral sanctions against Iran. It designates Iran's Quds Force a terrorism supporter, and calls out the Islamic Revolutionary Guard Corps (IRGC) for "support of weapons of mass destruction."
March 2008: The UN Security Council imposes a third round of sanctions. Iranian officials declare the sanctions illegal and coercive, and say Iran will continue to develop its nuclear potential.
September 2008: UN Security Council reaffirms commitment to sanctions, and to incentives if Iran agrees to halt uranium enrichment.