Hizb ut-Tahrir is an international pan-Islamist, Sunni "vanguard" political party whose goal is to combine all Muslim countries in a unitary Islamic state or caliphate, ruled by Islamic law and with a caliph head of state elected by Muslims.

The organization was founded in 1953 in Jerusalem by Taqiuddin al-Nabhani, an Islamic scholar and appeals court judge (Qadi) from the Palestinian village of Ijzim. Since then Hizb ut-Tahrir has spread to more than 40 countries, and by one estimate has about one million members.Hizb ut-Tahrir is very active in the west, particularly in the United Kingdom, and is also active in several Arab and Central Asian countries, despite being banned by most of the local governments.

Hizb ut-Tahrir's main base is in London and their presence is apparently tolerated by the British Government. This has reinforced the pejorative sobriquet of Londonistan.

Hizb ut-Tahrir believes a caliphate, an Islamic State, "will provide stability and security to all the people of the region, Muslims and Non-Muslims".The party promotes "an elaborate and detailed program for instituting an Islamist state that will "establish the laws of the Islamic Shariah and to carry the Da'wah of Islam to the world." It believes this "comprehensive solution" will provide "sincere leadership that cares for and protects its citizens from the colonial foreign policies of Bush and Blair" and bring an end to "US interventions, energy inspired wars, puppet (Muslim) governments and western values forced by the barrel of a gun." Hizb ut-Tahrir is strongly anti-Zionist and calls for "the dismantling" of the "illegal entity" of Israel.

Hizb ut-Tahrir has generated mixed opinions. Some observers believe it is a victim of unjust and untrue allegations of connections to terrorism. Others argue its stated opposition to violence is tactical and temporary, and it works to create an atmosphere conducive to terrorism by preaching hatred and by actions such as calling suicide bombers "martyrs" and talking of the need to "destroy the new crusaders," i.e. Western troops in Iraq.

The stated aim of Hizb ut-Tahrir is to unite all Muslim nations over time in a unitary Islamic state or caliphate, headed by an elected caliph. This it holds is a religious duty, "an obligation that Allah has decreed for the Muslims and commanded them to fulfill. He warned of the punishment awaiting those who neglect this duty." According to the BBC, the group "professes non-violence and calls for the return in Muslim majority countries to the caliphate that oversaw the golden age of Islam before European imperialism colonized the Middle East." According to GlobalSecurity.org, Hizb ut-Tahrir is a "secretive sectarian group," that is "not against violence as such. It is just against the use of violence now."

Another analyst quotes the work of Hizb ut-Tahrir founder Taqiuddin al-Nabhani to suggest that once Hizb ut-Tahrir has succeeded in creating a unified, transnational Islamist state it should press on to expand the state into non-Muslim areas. According to al-Nabhani's work The Islamic State, Muslims abroad `should work towards turning their land where Islam is not implemented, and which [thus] considered as Dar al-Kufr into Dar al-Islam".Al-Nabhani also noted that the original Muslim Ummah had presented `a world superpower in the face of the two major camps at the time, [the Persian and Byzantine Empires] whereupon she struck them both simultaneously, conquered their lands and spread Islam over almost the whole of the inhabited parts of the world at that time.`

Although hizb means party in Arabic, according to Zeyno Baran of the Washington, D.C. based Nixon Center think tank, Hizb ut-Tahrir hasn't registered as a political party nor attempted to elect candidates to political office in the countries where it is active. Nor does it engage in charitable or social service projects like groups affiliated with the Muslim Brotherhood.Hizb ut-Tahrir's focus is on "ideological struggle" to establish its vision of the caliphate in the minds of Muslims.

This is not true in all countries or throughout Hizb ut-Tahrir's history, as individual members of Hizb ut-Tahrir in their personal capacities have been involved in aid to needy Muslims in Indonesia and other countries,and has registered as a political organisation and stood for parliamentary seats in some countries. Hizb ut-Tahrir ran for office in Jordan in the 1950s when it was first formed, according to Suha Taji-Farouki, but was banned by the regime later. Kyrgyz Hizb ut-Tahrir members campaigned unsuccessfully for an affiliated candidate in Kyrgyzstan's national presidential election in July 2005, and have participated in municipal elections where their followers have won in a number of regions.

According to one analyst, Hizb ut-Tahrir

"plans its development in three stages... First they convert new members. Secondly, they establish a network of secret cells, and finally, they try to infiltrate the government to work to legalize their party and its aims."

A more sympathetic description of this strategy is that Hizb ut-Tahrir plans:

1. Establish a community of Hizb ut-Tahrir members who work together in the same way as the companions of Muhammad. Members should accept the goals and methods of the organization as their own and be ready to work to fulfill these goals.
2. Build public opinion among the Muslim masses for the caliphate and the other Islamic concepts that will lead to a revival of Islamic thought.
3. Once public opinion is achieved in a target country through debate and persuasion, the group hopes to obtain support from army generals, leaders, and other influential figures or bodies to facilitate the change of the government. The government would be replaced by one that implements Islam "generally and comprehensively", carrying Islamic thought to people throughout the world.

Talking to the BBC, an Indonesian party member described the "method used in Hizb ut-Tahrir" as "a change in thought patterns. We call it 'thought revolution'. When someone is given Islamic teaching — given the brilliant thinking of Islam — then they'll naturally undergo a thought revolution ... " According to the BBC, "unlike many other Islamist movements here, Hizb ut-Tahrir seems less interested in a broad mass following than a smaller more committed core of members, many of them drawn from Indonesia's educated middle classes." The party has been called a "vanguard party" for its interest in achieving power through "hundreds of supporters in critical positions" rather than "thousands of foot soldiers"though at least one of its leaders (Jalaluddin Patel) has denied HT is such a party.

Hizb ut-Tahrir's organisation is said to be strongly centralized with its central leadership based in Palestine. Underneath its center are "national organisations or wilayas, usually headed by a group of 12, control networks of local committees and cells." New members "spend at least two years studying party literature, under the guidance of mentors," before taking an oath of loyalty to the party. "A parallel, separate structure exists for women, who are encouraged to become fully active members.

The basic unit of the party is a cell of five members, the leader of which is called a mushrif. Only the mushrif knows the names of members of other cells