Hamas ("zeal" in Arabic) is the acronym for Harakat al-Muqawima al-Islamiya, or "Movement of Islamic Resistance." It was founded in the Gaza Strip, shortly after the outbreak of the first Palestinian intifada in December 1987, by Palestinian members of the Muslim Brotherhood (an organization founded in the 1920s in Egypt, whose emergence in the Gaza Strip was initially welcomed by Israeli military authorities as an alternative to the secular nationalism of the PLO).
Hamas is divided into a public branch that extends social welfare - schools, day care, summer camps for youths, medical clinics - to the Palestinian community, and an underground military branch called the Izz ed-Deen al-Qassam Brigades (named after a leader in the first Palestinian armed revolt against the British and the Zionist movement from 1936-39, who was killed by British troops).
The stated aim of Hamas is to establish an Islamic state in all of Palestine, including what is today Israel, through violence if necessary. However, a number of Hamas leaders have indicated that full Israeli withdrawal from the Occupied Territories would justify a long-term truce, and abandonment of violent resistance. A number of Hamas leaders have been assassinated by Israel.
Hamas is not a member organization of the PLO, and has opposed the Oslo accords. It initially treated the Palestinian Authority - a product of the accords - as illegitimate, and refused to participate in the first PA elections in 1996. However, it fielded candidates in municipal elections in January 2005, winning majorities on 28 of 84 town councils in the Gaza Strip and West Bank.
Hamas members also participated in elections for the Palestinian Legislative Council held in January 2006, although running under the banner of the "Change and Reform Party." The new party promised reforms of the Palestinian Authority and more steadfast support of Palestinian rights to freedom and independence, but did not reiterate Hamas's goal of establishing an Islamic state in Palestine. Change and Reform Party candidates took 74 of 132 seats in the Palestinian Legislative Council, and the party, under the leadership of Ismail Haniyeh, formed a new Palestinian government.
Following the elections, factional violence between Fatah and Hamas in 2007 left Hamas in control of governance in the Gaza Strip, with a Fatah-led PA functioning only in the West Bank. In April 2014, the two parties signed a reconciliation agreement and in June 2014 a new technocratic government was formed, reuniting the West Bank and Gaza Strip under the PA.