By Sebastian Usher
BBC world media correspondent
The Iranian leadership reinforces its message through the media
The authorities in Iran are highly conscious of the power of the media.
They use a two-pronged approach. At home, they enforce controls on the media that stifle freedom of expression, although there are still outlets on TV, radio, in the press and on the internet that provide alternative points of view and are available to ordinary Iranians.
Abroad, Iran harnesses satellite TV and radio to get its views across in a variety of languages - Arabic in particular - in an effort to influence opinion in neighbouring countries and the wider world.
In Iran, there is no escape from the control that the state exerts over the media.
Broadcasting is run by the authorities. It reflects the views of the Supreme Leader Ayatollah Ali Khamenei and his allies in the conservative clerical establishment.
There are no private, independent broadcasters allowed to operate inside the country.
The internet has provided a big challenge for the Iranian authorities in its efforts to control information
The Islamic Republic of Iran Broadcasting controls TV and radio. It is dominated by conservatives, and has often been criticised by Iranian reformists for its conservative bias.
It often ignored the activities and statements of the former president - and reformist leader - Mohammed Khatami. In recent elections, reformists criticised state TV and radio for blatantly favouring conservative candidates.
But state TV and radio are not the only broadcasters available in Iran. Satellite ownership may be illegal, but the law is only intermittently enforced.
The result is that Iranians can see and hear non-state controlled media from outside the country.
A flood of Farsi satellite stations is broadcast from the Iranian diaspora, particularly in the US. Most of these stations are shoestring affairs - amateurish and ramshackle - but they do provide very different viewpoints from those on state media.
Some exist solely to attack the Iranian authorities and are run by exiles from the Iranian revolution. They have covered protests in Iran, showing images that Iranians would never see on state TV.
Voices of dissent face strict state controls
The Iranian authorities are reported to have tried to jam the signals of these stations at especially sensitive times. Other channels profess to be non-political and concentrate on entertainment.
Iranians can also listen to foreign broadcasters that run Persian language services.
They include the BBC, Voice of America, Radio France Internationale and Deutsche Welle. Recently, Iran was reported to have blocked the BBC Persian service on the internet, which receives millions of hits.
The internet has provided a big challenge for the Iranian authorities in their efforts to control information.
It is now the main forum for dissident voices in Iran. Millions of Iranians have access to the internet and there are thousands of Iranian blogs.
In response, the government has adopted one of the most sophisticated internet censorship systems in the world - comparable to that used in China.
Only a handful of newspapers remain that voice alternative views to the conservative establishment
Officially, internet filtering is to block what the Iranian government sees as pornographic or immoral material. In practice, it also clearly tries to block sites with political content.
One of the reasons why the internet has become such an important medium for opposition or reformist voices in Iran is due to the crackdown on the press that hardliners have carried out in the past few years.
Only a handful of newspapers remain that voice alternative views to the conservative establishment. All newspapers have to be licensed.
The press law bans articles that "violate Islamic principles" or "might damage the foundation of the Islamic Republic".
Most of the key reformist newspapers have been closed down under the law and a number of journalists and editors imprisoned.
To bypass press censorship, reformist and opposition journalists have increasingly moved onto the internet, opening news sites and blogs.
But thanks to Iran's internet filtering system, the most prominent of these have periodically been blocked, with reports that hundreds - possibly thousands - of sites have been blacklisted.
Despite the authorities' efforts, Iranians are able to receive information that challenges what state broadcasters say from a variety of sources - whether by satellite, radio, the press or online.
But all of these face constraints and come under sporadic attack from the hardline conservative establishment, which dismiss them in any case as part of a foreign conspiracy to bring the country down.
Influence on Iraq
On the international stage, Iran tries to combat other media sources with its own relatively advanced satellite and radio stations. The most significant of these is Al Alam - The World - a 24-hour news channel in Arabic, which it launched as Saddam Hussein's regime was ousted in Iraq.
Sophisticated media control bolsters support for state and foreign policy
Iran stole a march on everyone else by launching Al Alam with a powerful transmitter near the border with Iraq as the dust was still settling over the second Iraq war.
Its influence was felt immediately. It filled a void, as many Iraqis did not have satellites or access to them in the wake of Saddam Hussein's defeat.
That meant that Al Alam - which could be received as a terrestrial channel across the country - was present in many Iraqi homes before Al Jazeera or other Arab satellite news channels could get a look in.
Its air of professionalism and the visceral impact of its images and reports won it a good proportion of Iraqi viewers. It undeniably helped spread Iran's influence in post-Saddam Iraq.
But it is not the only TV station broadcasting from Iran to the outside world.
Iran's rulers have invested heavily in such channels - one broadcasts specifically to the Iranian diaspora; another, Sahar TV, broadcasts in a variety of languages, including English, French, Kurdish and Urdu.
A state-run radio station also broadcasts in about 30 languages. And that's not to mention the Lebanese channel, Al Manar - known as Hezbollah TV - which has received Iranian support.
All of this shows just how seriously Iran takes the role of the media in trying to influence and stir up opinion in the Arab world and beyond - just as it tries to control the information available to its own people within the country.