The United States has launched military action against Iran following weeks of threats and in the aftermath of a deadly crackdown on protests.
Iran has been ruled by a clerical system headed by a supreme leader ever since the 1979 Islamic revolution that toppled the pro-Western Pahlavi dynasty.
Here is a breakdown of the key elements of Iran's ruling apparatus:
Supreme leader
Iran's supreme leader is chosen for life by the elected Assembly of Experts, and in theory is overseen by the top clerical body, but in practice, he has the final word on all foreign and domestic policy.
He names the leaders of top institutions, including the chief justice, half of the powerful Guardian Council, military commanders and the head of the state broadcaster.
As commander-in-chief, he controls the security, military and intelligence apparatuses.
Supreme Leader Ayatollah Ali Khamenei, 86, took up the post in 1989 after the death of revolutionary leader Ayatollah Ruhollah Khomeini.
Seeing off crises throughout his rule with a mixture of repression and strategic manoeuvres, Khamenei has faced steep challenges, including last year's war with Israel, the weakening of Iran's regional proxies and recent mass protests.
Elected officials
Iranians over 18 have the right to vote for the president, parliament and the Assembly of Experts, but their choices are limited by clerical oversight, as candidates must be approved by the 12-member Guardian Council.
The power of the president, elected for a four-year term, pales compared to the supreme leader's, though the role is high profile and public, while Khamenei appears relatively rarely.
The president steers the country's economy, a key challenge in sanctions-hit Iran, and the latest protest movement was sparked by anger over persistently dire economic conditions.
Current President Masoud Pezeshkian is among the more moderate figures to have had the job, and has been allowed to attempt cautious reform and a rapprochement with the West.
He can only go, however, as far as the supreme leader allows, especially in the hardline confrontation with the "great Satan" the United States and its regional ally Israel.
The president appoints multiple vice presidents and a cabinet, which is confirmed by the single-chamber, 290-seat parliament.
Legislation passed by the conservative-dominated parliament must be approved by the Guardian Council before it becomes law.
Disputes over the approval of a law are mediated by the Expediency Council -- made up of senior Islamic republic figures, who also advise the supreme leader.
Armed forces
Iran's armed forces are made up of the ideological army of the Islamic republic, the Islamic Revolutionary Guard Corps (IRGC), and a regular army.
They report to the supreme leader through Iran's senior military body the Armed Forces General Staff.
The IRGC is celebrated as a key pillar of the theocratic system, tasked with preserving the future of the revolution.
A vast and complex organisation, its well-resourced branches reach into economics, politics and society.
Accused by the West of militant activity abroad and serial rights violations at home, some of its top brass were among the military figures killed during the 12-day war with Israel in June.
These losses revealed Israel's deep intelligence penetration of the Islamic republic, including within the IRGC, but the slain commanders were quickly replaced from within the ranks.
Iran's national security decisions are driven by the Supreme National Security Council, guided by the supreme leader's foreign policy.
The body is chaired by the president and includes key governmental, judicial and military figures, and is fronted by the high-profile secretary -- currently establishment mainstay Ali Larijani -- who is one of two representatives of the supreme leader on the council.
After the 12-day war, the SNSC established a new body focused on enhancing Iran's armed forces and defence strategies, the National Defence Council, headed by former defence minister and adviser to the supreme leader, Ali Shamkhani.