(CNN) -- Here's a look at what you need to know about the 1979 Iran hostage crisis, in which 52 U.S. citizens were held captive for 444 days.
Timeline: 1978 - Shah Mohammed Reza Pahlevi's authoritarian rule sparks demonstrations and riots. Martial law goes into effect.
January 16, 1979 - The Shah goes into exile in Egypt.
February 1, 1979 - Ayatollah Khomeini returns to Iran after 14 years in exile, to lead the country.
October 22, 1979 - The Shah arrives in the U.S. for medical treatment for lymphoma.
November 4, 1979 - About 500 Iranian students seize control of the U.S. embassy in Tehran and take 90 people hostage including 66 Americans working in the embassy. They demand the extradition of the Shah from the U.S. in exchange for the hostages.
November 5, 1979 - The Iranian government announces the cancellation of military treaties with the U.S. and the Soviet Union, treaties that would permit U.S. or Soviet military intervention.
November 6, 1979 -Premier Mehdi Bazargan and his government resign, leaving Ayatollah Ruhollah Khomeini and the Iran Revolutionary Council in power.
November 7, 1979 - President Jimmy Carter sends two envoys, former Attorney General Ramsey Clark and William Miller, to Iran to discuss U.S.-Iranian relations and to seek release of the hostages. Ayatollah Khomeini refuses to meet with them.
November 12, 1979 - Foreign Minister Abolhasan Bani-Sadr issues a set of demands to obtain the release of the hostages, including the return of the Shah and cessation of U.S. interference in Iranian affairs.
November 14, 1979 -President Carter orders Iranian bank assets in the U.S. frozen.
November 17, 1979 - Khomeini orders the release of eight African-American and five female hostages.
November 19, 1979 - The U.S. asks the United Nations Security Council to warn Iran over putting the remaining hostages on trial, saying it was a violation of international law. The United Nations refuses.
November 29, 1979 -The United States files suit against Iran in the International Court of Justice.
December 4, 1979 - The United Nations Security Council approves a resolution calling for Iran to release the hostages.
December 15, 1979 - The Shah leaves the U.S. for treatment in Panama. He returns to Egypt on March 25, 1980.
January 28, 1980 - Canadian diplomats help six American embassy employees who had not been captured flee Iran.
April 7, 1980 -The U.S. imposes sanctions and cuts diplomatic ties with Iran.
April 24, 1980 - Eight U.S. servicemen are killed when a helicopter and a transport plane collide during a failed attempt to rescue the hostages.
July 11, 1980 - One hostage is released because of illness. This brings the final number to 52.
September 12, 1980 - Ayatollah Ruhollah Khomeini sets new terms for the hostages' release revolving around the late Shah's financial assets which Iran estimated to be $32 billion.
November 10, 1980-January 8, 1981 - Deputy Secretary of State Warren Christopher and his delegation work through intermediaries in Algeria to respond to the Iranian conditions set forth in September to negotiate the release of the hostages.
January 19, 1981 - The U.S. and Iran sign an agreement to release the hostages and unfreeze $8 billion dollars of Iranian assets.
January 20, 1981 - Ronald Reagan is sworn in as president of the U.S.
January 20, 1981 - The remaining 52 U.S. hostages are released and flown to Weisbaden Air Base in Germany.