(CNN) -- Hamas is an Islamic fundamentalist organization whose military wing has admitted responsibility for terrorist attacks against Israeli civilians and soldiers.
Hamas supporters wave flags and shout slogans in Gaza on December 14 to mark the group's 21st anniversary.
The group came into being in December 1987, growing out of the Muslim Brotherhood, the religious and political organization founded in Egypt. Its goal is an Islamic fundamentalist Palestinian state. It is considered a terrorist organizations by Israel and the United States.
Hamas is an acronym for "Harakat Al-Muqawama Al-Islamia" or Islamic Resistance Movement, in English. The group was primarily a religious and charitable organization between the 1960s and 1980s. It has wings devoted to religious, military, political and security activities.
Hamas has an annual budget of $70 million, according to the Council on Foreign Relations. It gets financial support from expatriate Palestinians, private donors in the Middle East, Muslim charities in the West, and Iran.
Here are some notable events in its 21-year history:
1988 - The covenant of the Islamic Resistance Movement is published. The group presents itself as an alternative to the PLO.
1989 - An Israeli court convicts Hamas leader Sheikh Ahmed Yassin of ordering Hamas members to kidnap and kill two Israeli soldiers.
April 1994 - Hamas orchestrates its first suicide bombing. Five are killed in the Israeli city of Hedera.
February to March 1996 - The Palestinian Authority cracks down on Hamas, after a series of Hamas-orchestrated suicide bombings in Israel kill more than 50 people. Palestinian President Yasser Arafat condemns the bombings, referring to them as "a terrorist operation." Later, the PNA arrests approximately 140 suspected Hamas members.
1997 - Hamas leader Sheikh Ahmed Yassin is released from prison.
1999 - King Abdullah of Jordan closes down Hamas headquarters in Jordan.
2001 - The U.S. State Department lists Hamas on its official list of terrorist groups.
June 12, 2003 - A suicide bomber disguised as an ultra-orthodox Jew detonates himself on a Jerusalem bus, killing 16 Israelis. Hamas claims responsibility.
August 20, 2003 - A suicide bomber detonates himself on a bus killing at least 20 Israelis. Hamas and Islamic Jihad claim responsibility.
January 2004 - The first Hamas female suicide bomber kills four Israelis at Erez crossing in a joint operation with the Al-Aqsa Martyrs Brigades.
March 14, 2004 - Hamas and the Al-Aqsa Martyrs Brigades claim responsibility for a double attack at the Israeli port of Ashdod that kills 10 Israelis.
March 22, 2004 - Hamas leader Yassin is killed by Israeli air strikes.
March 23, 2004 - Dr. Abdel Aziz Rantisi is named as Yassin's successor.
April 17, 2004 - Rantisi is killed by an Israeli air strike on his car.
August 31, 2004 - The Islamic militant group Hamas claims responsibility for deadly simultaneous explosions on two buses in the southern Israeli city of Beer Sheva that killed at least 14 people and wounding more than 80.
September 26, 2004 - A leading member of Hamas, Izz Eldin Subhi Sheikh Khalil, is killed by a car bomb as he leaves his home in Damascus, Syria.
December 12, 2004 - An attack at a checkpoint on the border between the Gaza Strip and Egypt kills five Israelis. Hamas claims responsibility.
January 14, 2005 - A bomb at the Karni crossing at the Israel-Gaza border kills six Israelis. Hamas claims responsibility.
January 25, 2006 - Hamas, running as the "Change and Reform Party," participates for the first time in Palestinian parliamentary elections. The group is fielding 62 candidates.
January 26, 2006 - Hamas wins a landslide victory in the Palestinian legislative elections. Hamas wins 76 seats, and Fatah 43 seats in the 132-seat Palestinian Legislative Council, giving Hamas a majority.
March 29, 2006 - The new Palestinian Prime Minister, Ismail Haniya, and his cabinet are sworn in. The governments of the United States and Canada say they will have no contact with the Hamas-led Palestinian government.
June 25, 2006 - Hamas militants attack an Israeli military post and kill two soldiers. A third, Gilad Shalit, is kidnapped. The Palestinian government denies any knowledge of the attack.
Early June 2007 - After a week of battles between Hamas and Fatah, Hamas seizes control of Gaza. Read a profile of Gaza
June 14, 2007 - Palestinian Authority President Mahmoud Abbas dissolves the government and dismisses Ismail Haniya as Prime Minister. Haniya rejects this and remains the de facto leader in Gaza.
April 18-19, 2008 - Former U.S. President Jimmy Carter meets with exiled Hamas leader Khalid Meshaal, in Damascus, Syria.
June 2008 - Cease-fire truce between Hamas and Israel negotiated by Egypt goes into effect. Hamas agrees to stop firing rockets at Israeli border communities and Israel will allow limited trade into and out of Gaza. The cease-fire has a six-month deadline.
December 19, 2008 - Hamas formally ends cease-fire with Israel. Attacks between the two had continued the entire time to some degree, escalating more in November.
From December 24, 2008 - The rocket attacks from Hamas increase and so do the retaliation air strikes from Israel. See photos of Gaza in crisis »