Conscription exists since 1925. 
The present legal basis of conscription is the 1984 Military Service Act, plus various decrees issued since than.
Military service is performed in the armed forces and the Pasdaran (Islamic Revolutionary Guard), which was established in 1979 by Ayatollah Khomeini, its prime responsibility being to preserve internal security. Since 1989 both the Pasdaran and the regular armed forces are under Ministry of Defence jurisdiction, but under a different command. In 1995 the Iranian authorities were thought to have started to reduce and reorganise the Pasdaran, but it is no known whether they succeeded - the Pasdaran is traditionally quite autonomous. 
There are also several paramilitary forces, such as Ashura, a militia established by the government in 1993; Hezbollahi, radical Islamic militants, tolerated by the government and Basiji, which mostly consists of young people. No information is available on the recruitment methods of these paramilitary forces. 
All men between the ages of 18 and 50 are liable for military service, between 18 and 60 in time of emergency. 
Military service lasts for two years. It was reduced from 28 months in 1988 after the end of the war with Iraq. 
The 1984 law provides for reserve service for those up to the age of 50; and up to 60 in times of general mobilisation. Since 1989 reservist obligations are thought not to be enforced in practice. 
postponement and exemption
Postponement is possible for students. Students must be available for military service as soon as they have completed their studies. 
Students who continue their studies abroad and who pay their own expenses are exempted. PhDs and men with BAs who left Iran before March 1990 may get exempted on paying a fee of USD 16,600,-. 
Exemption is possible for medical reasons, for domestic reasons (if an individual is the sole family breadwinner) and in the case of 'martyrs of the revolution' (those having a brother or father who died in the Iran-Iraq war).  
Men who left Iran after 1990 may get exempted on paying a fee of USD 1,000-3,000. 
All men must register for medical examination at a local recruitment centre in the year they become 18. An age-group of conscripts is called up for medical examination via announcements in the media. After medical examination those found fit to serve receive a military document with their call-up date. Call-up for military service usually takes place at the age of 18. 
As the number of liable conscripts exceeds the number of recruits actually needed, recruitment is by ballot. Officials of the regular armed forces and the Pasdaran set quotas for the number of recruits required. When, after the ballot, a conscript is called up he may choose if he wants to serve in the Pasdaran or in the regular armed forces. Many apparantly want to serve in the Pasdaran, given the incentives and benefits this entails. But, depending on the conscripts' skills, his choice may be disregarded by the Pasdaran recruitment officers. Politically suspect individuals are thought to be less likely to be recruited by the Pasdaran.  
Those who are not recruited are granted deferment from for a few months to a year.   
2 Conscientious objection
The right to conscientious objection is not legally recognized and there are no provisions for substitute service.  
3 Draft evasion and desertion
Draft evasion and desertion are punishable under the 1992 Law on Punishment of Crimes Concerning the Armed Forces, which prescribes different penalties for permanent and for temporary members of the armed forces. The following information concerns the possible punishment for temporary members of the armed forces (conscripts).
Absence without leave for more than 15 days without a valid reason is punishable by six months' to two years' imprisonment and/or 12 months extension of military service;
Desertion is punishable by two to 12 months' imprisonment in case the deserter surrenders himself to the authorities.
Those who avoid call-up for military service are considered deserters. 
In 1996 the Tazi'rat (the Islamic criminal code) was amended to prescribe harsher punishments for several offences. Although draft evasion and desertion are not specifically mentioned in the Tazi'rat, it seems likely that some articles, notably arts. 504 and 509, apply to draft evasion and desertion.  
According to art. 504: "Whoever manages to incite the armed forces, or who in one way or another assists the armed forces, to rebellion, desertion, surrender or non-performance of their military duties shall be considered a Muhaarib if he intended to overturn the government or to enable the defeat of own forces by the enemy; otherwise, if the actions taken by him have been effective he will be sentenced to from two to ten years' imprisonment, and if they are not, he will be sentenced to six months' to three years' imprisonment." (A Muhaarib is someone who takes up arms against the Islamic government).
According to art. 509: "Whoever commits one of the crimes against the internal or external security mentioned in this chapter during the war will receive the maximum sentence for such a crime."
There is considerable monitoring of draft evasion and desertion. All who have completed their military service get a certificate - needed for various practical matters, such as obtaining a passport or driving licence, getting a job in some state enterprise. 
According to a 1983 law all men must, on certain occasions, be able to prove they have performed military service. Inability to produce the certificate can lead to difficulties over getting offered certain jobs. 
Draft evaders and deserters who have been punished and eventually completed their military service, may face a delay of from several months to ten years over receiving this certificate. The delay is the shortest for draft evaders in peacetime who have returned voluntarily and the longest for draft evaders in wartime. 
Those granted postponement of military service may leave the country only in exceptional circumstances and they must pay a deposit. Foreign travel permits are valid for only up to three months. Airport authorities have lists of those forbidden to leave the country, and passports are thoroughly checked by the police and security forces. Individuals granted exemption get a document certifying that they may leave the country. 
Due to the closedness of Iranian society, detailed information about the punishment of draft evaders and deserters is difficult to obtain.
According to one source, draft evaders and deserters are particularly apt to face punishment if they have deserted for political reasons, if they have been politically active in the past or if they have deserted previously during the war with Iraq. 
Several amnesties for draft evaders and deserters have been announced in the past.
In June 1992 an amnesty was announced, which prescribed that draft evaders and deserters who availed themselves to the authorities before July 1992 had to perform military service for the usual length of time. It is not known how this amnesty functioned in practice. 
Between July 1992 and March 1993 there was an amnesty in force for draft evaders and deserters who had left the country. It exempted them from further military service provided they paid a fine, the amount depending on the number of years they had received state education. It is thought that draft evaders and deserters have indeed benefited from this amnesty.  
In May 1996 an amnesty was announced, which reduced the prison sentences of military offenders and released them from prison by 23 May 1996. It is not clear if this amnesty applied to draft evaders and deserters. 
6 Annual statistics
The armed forces are 450,000-strong - that is, 0.71 percent of the population.
Every year about 580,000 men reach conscription age. There are 320,000 conscripts in the armed forces. 
The paramilitary forces are about 350,000-strong. 
 UNHCR Centre for Documentation on Refugees 1995. Background Paper on Refugees and Asylum Seekers from Iran. UNHCR, Geneva.  UN Commission on Human Rights, 1996. Report on the situation of human rights in the Islamic Republic of Iran, prepared by Maurice Copithorne, 21 March 1996. United Nations, Geneva.  German Ministry of Foreign Affairs 1995. Lagebericht Iran, 1 September 95. Auswäriges Amt, Bonn.  Amnesty International (Dutch Section) 1994. Letter to Staatssecretaris van Justitie, 16 December 1994. AI, Amsterdam.  Amnesty International (Dutch Section) 1989. Letter to VluchtelingenWerk, 1 September 1989. AI, Amsterdam.  Dutch Ministry of Foreign Affairs 1996. Ambtsbericht, 1 May 1996. BuiZa, Den Haag.  Dutch Ministry of Foreign Affairs 1991. Ambtsbericht, 24 June 1991. BuiZa, Den Haag.  Immigration and Refugee Board 1997. Human rights in Iran: Update on selected issues. DIRB, Ottawa.  UN Commission on Human Rights 1997. The question of conscientious objection to military service, report of the Secretary-General prepared pursuant to Commission resolution 1995/83. United Nations, Geneva.  Dutch Ministry of Foreign Affairs 1997. Ambtsbericht, 5 June 1997. BuiZa, Den Haag.  Institute for Strategic Studies 1997. Military Balance 1997/98. ISS, London.  'Khamene'i approves amnesty, reduction in sentences for military offenders', Voice of the Islamic Republic of Iran, 21 May 1996.  DIRB, 26 January 1996.  DIRB, 28 November 1995.  DIRB, 23 May 1997.  Amnesty International 1991. Conscientious objection to military service. AI, London.
The Iranian parliament (Majlis) has passed a new bill to cut military service in the country by 2 to 10 months for conscripts with university degrees, Iranian Press TV reported on 30 June 2009. Presently, military service lasts generally 18 months, but there are shorter terms for college graduates.
According to the latest Majlis ratification, military service for conscripts with a PHD falls 10 months. Master and bachelor graduates will serve 8 and 6 months lesser respectively.