The very structure of Iran's government is built upon a foundation split by a power struggle between reformists and Islamic hard-liners. According to Iran's constitution, its supreme leader, Ayatollah Ali Khamenei, who succeeded revolutionary leader Ayatollah Ruhollah Khomeini, holds the majority of the power. Elected leaders, including President Mahmoud Ahmadinejad and members of parliament, hold much less authority.

Supervisory bodies -- including the Expediency Council, Council of Guardians and the Assembly of Experts -- also carry broad responsibilities to monitor the government and ensure the legislation follows both the constitution and Islamic law.

Iran's constitution was written in 1979 and amended in 1989.

Elected
President
The president is the second highest-ranking government official in Iran. Elected by popular vote to a four-year term, they are limited to two consecutive terms. The president appoints and supervises the Cabinet, coordinates government decisions, and selects government policies to be considered by the parliament. Above the president is Iran's supreme leader, who has control over the military, judiciary and any critical policy matter, both domestic and foreign. The president sets the country's economic policies and has a nominal rule in other governmental matters including security and intelligence.

Council of Ministers
Although not elected directly, members of the Iranian Cabinet -- also known as the Council of Ministers -- are selected and supervised by the president and are also subject to confirmation by the parliament. The supreme leader holds influence in the decision-making of some of the most critical posts. In all, some eight vice presidents and 22 Cabinet ministers serve under the president.

Parliament
The parliament, known as the Majlis or National Assembly, has 290 members elected by popular vote to four-year terms. Each member represents a geographic constituency. The Council of Guardians has particular power over the Majlis through its authority to approve or disqualify potential parliamentary candidates.

The parliament introduces and passes laws that are ultimately subject to approval from the Council of Guardians. The Expediency Council mediates between the Council of Guardians and the parliament when they disagree on an issue.

The legislative body has the power to summon and impeach Cabinet-level ministers, including the president. It is also responsible for approving the country's budget and ratifying international treaties. The parliament is often a key venue for confrontation between reformer politicians and their conservative counterparts.

Assembly of Experts
The Assembly of Experts is composed of some 86 clerics, whom the public elects for eight-year terms. The group usually meets for one week once or twice a year. As with Iran’s other publicly elected bodies, the Council of Guardians must approve all candidates for the Assembly of Experts.

The Assembly of Experts appoints the supreme leader and reconfirms him periodically. The group is responsible for monitoring his performance and removing him if necessary.

Appointed or Approved
Supreme Leader
The supreme leader is Iran's top decision-maker, and has final say in all matters of state. According to Iran's constitution, the supreme leader is responsible for supervising the "general policies of the Islamic Republic of Iran" and directs all the country's foreign and domestic policy. The supreme leader also controls the military and Iran's intelligence operations. He alone has the power to declare war. He also appoints leaders of the judiciary, the state media, the Islamic Revolutionary Guard Corps and six of the 12 members of the Council of Guardians, a powerful oversight committee.

The supreme leader is represented throughout the government through representatives that serve as field liaisons. These representatives have the authority to intervene in any matter on the supreme leader's behalf.

Only two men have held the position of Iran's supreme leader: Ayatollah Ali Khamenei and Ayatollah Ruhollah Khomeini, the father of the Iranian Revolution.

Council of Guardians
Composed of six religious members and six lawyers, the Council of Guardians is a highly influential part of the Iranian government. The supreme leader appoints the six theologians, and the judiciary nominates the six legal experts. The nominations are then subject to parliamentary approval.

The council has wide influence. The group vets all bills the legislature passes, to ensure they adhere to the constitution and Islamic principles. If the council rejects a bill, the lawmakers must revise it. At times the council has struck down up to 40 percent of laws parliament has passed. The council also approves all candidates for parliament, the presidency and the Assembly of Experts.

Armed Forces and National Security
The Iranian military includes two groups: the regular army and the Islamic Revolutionary Guard Corps. The regular army defends the country and maintains order, while the Revolutionary Guard protects the Islamic revolution and its achievements. The supreme leader appoints all top military commanders, and they report directly to him.

The president heads the Supreme National Security Council, which includes the speaker of parliament, head of judiciary, chief of the combined general staff of the armed forces, key cabinet ministers and commanders of the regular military and Revolutionary Guard. The president guides the council in executing the supreme leader's foreign policy directives.

Another element of Iran's national security is the Ministry of Intelligence and Security, about which little is publicly known. According to law, the ministry is responsible "gathering, procurement, analysis, and classification of necessary information inside and outside the country." A law also specifies that the head of the ministry be a cleric.

Judiciary
The supreme leader appoints the head of the judiciary, who in turn appoints the Supreme Court head and the top public prosecutor. After the Islamic revolution, the Supreme Court revoked all laws deemed un-Islamic and new laws were established based on Sharia, which is law framed around interpretations of the Islamic holy text, the Koran.

The judiciary nominates the six lay members of the Guardian Council who are usually lawyers. Public courts deal with civil and criminal offenses. Separate "revolutionary" courts try other categories of offenses such as crimes against national security or offenses that threaten the Islamic republic. A Special Clerical Court, which is accountable to the supreme leader and -- outside of the judicial structure -- crimes allegedly committed by clerics and occasionally lay people.

Decisions from the revolutionary courts or the clerical court are final and cannot be appealed.

Expediency Council
The Expediency Council, which Ayatollah Khomeini created in 1988, wields influence through its role as national policy adviser to the supreme leader. The council also mediates legislative disputes between the parliament and the Guardian Council.

Its members include heads of the three government branches, the clerical members of the Guardian Council and various other members appointed by the supreme leader for three-year terms. Cabinet members and parliamentary leaders also serve as temporary members when issues under their jurisdictions are under review.

Sources: U.S. Department of State Background Notes, Iran Chamber Society: "The Structure of Power in Iran," BBC: "Iran: Who Holds the Power?"

-- Compiled by Maureen Hoch for the Online NewsHour