The Islamic revolution of 1979, during which the monarch, Shah Mohammed Reza Pahlavi, was driven out of the country, brought the Shiite clergy to power with Ayatollah Ruhollah Khomeini as its charismatic leader. Following the revolution, Iran adopted a constitution based on Ayatollah Khomeini's theory of Islamic government. The constitution ratified by popular referendum established a theocratic (from ancient Greek, literally meaning "the rule of God") republic and declared as its purpose the establishment of institutions and a society based on Islamic principles and norms, adopting the shari'a (Islamic law) as the basis for the country's legal system. The Constitution of the Islamic Republic provided for a Vali-ye Faqih , a Supreme Leader of the Islamic Revolution. Since the death of Ayatollah Khomeini, in 1989, this office has been held by Ayatollah Ali Khamenei. The Supreme Leader still enjoys primary control of many organs of the state and has the right to appoint key officials such as heads of the judiciary, the broadcast media, the armed forces, and various revolutionary bodies, as well as the power to supervise the overall policies of the regime.
The 1979 constitution created an Islamic Consultative Assembly called the Majlis, Iran's most democratic legislature in its history. Its 290 members are elected by universal adult suffrage—men and women from the age of 16 are eligible to vote—and serve for 4-year terms. The Majlis develops and passes legislation that is reviewed for adherence to Islamic and constitutional principles by a Council of Guardians, which consists of 6 clerical members. These are appointed by the Supreme Leader and 6 jurists, who in turn are appointed by the head of the judiciary and approved by the Majlis. The constitution provides the Council of Guardians with the power to disqualify candidates for elective offices based on a set of requirements, including the candidates' ideological beliefs.
The country's president is elected by popular vote to a 4-year term and has the power to appoint a cabinet known as the Council of Ministers, with the approval of the legislature. Mohammad Khatami was elected in elections held on 3 August 1997.
Political parties, legalized in 1998 after a 13-year ban, are still at an early stage of development. Nevertheless, factions within the ruling hierarchy, particularly in the Majlis, are increasingly visible. While these are most often defined broadly as "reformist" or "conservative," political allegiances do exist based on patronage, loyalties, specific interests, and the exchange of favors.
Several agencies share responsibility for internal security, including the Ministry of Intelligence and Security, the Ministry of Interior, and the Revolutionary Guards, a military force that was established after the revolution. Paramilitary volunteer forces known as Basijis, and groupings, known as the Ansar-e Hezbollah (Helpers of the Party of God), who often are aligned with specific members of the leadership, act as watchdogs, intimidating and physically threatening demonstrators, journalists, and individuals suspected of counter revolutionary activities. According to Amnesty International and Human Rights Watch, both regular and paramilitary security forces committed numerous serious human rights abuses. Iranians also suffer from violations of freedom of expression. Iran's conservative-dominated judiciary waged an extensive campaign against the local reformist press, closing newspapers and prosecuting critical journalists throughout 2000.