:For the religion of Islam, see Islam. :For the book about Ed Husain's five years as an Islamic fundamentalist, see The Islamist. Islamism (Arabic: al-'islāmiyya) is a term that denotes a set of political ideologies holding that Islam is not only a religion but also a political system; that Muslims must return to their roots of their religion, and that they must become unified.

Islamism is a controversial term and definitions of it vary. Leading Islamist thinkers emphasized the introduction of sharia, or Islamic law, into modern society, and the belief that western military, economic, political, social, or cultural influences in the Muslim world were un-Islamic and should be replaced by purely Islamic influences. They also espouses pan-Islamic political unity.

Some sources suggest that its tenets urge "support for identity, authenticity, broader regionalism, revivalism, [and] revitalization of the community," while others define it as "an Islamic militant, anti-democratic movement, bearing a holistic vision of Islam whose final aim is the restoration of the caliphate." Attributes of sharia law supported by many Islamists include "enforcement of Islamic punishments, including prohibitions on taking interest, playing music, showing television," and enforcing traditional dress and prayer attendance.

Central figures of modern Islamism include Muhammad Iqbal, Jamal al-Din al-Afghani, Abul Ala Maududi, Sayyid Qutb and Ayatollah Khomeini. The term Islamism encapsulates a variety of movements and groups, from reformists who seek change within the scope of the electoral process to antidemocratic radicals who espouse violence against dissenters. Moderate Islamist voices that accept the democratic process include the Justice and Development Party of Turkey and Tunisian author and reformer Rashid Al-Ghannouchi. Lebanon's Hezbollah participates in elections, but also endorses armed attacks against Israel on behalf of its Palestinian constituents, leading to its often being identified alternately as a political party by its sympathizers and as a terrorist organization by its critics. Groups such as the Jamaat-e-Islami of Pakistan and the Sudanese Muslim Brotherhood favored a top-down road to power by military coup d'état. The radical Islamists al-Qaeda and Egyptian Islamic Jihad oppose democracy entirely, and emphasize violent jihad, supporting the use of attacks on civilians and takfir on fellow Muslims. One of the major divisions in Islamism is between the fundamentalist "guardians of tradition" of the Salafism or Wahhabi movement, and the "vanguard of change" centered on the Muslim Brotherhood.

This usage is controversial. Those labeled Islamists often, if not always, oppose use of the term, maintaining that they are simply Muslims, and that their beliefs are a straightforward expression of Islam as a way of life. Some people find it troublesome that a word derived from "Islam" is applied to organisations they consider radical and extreme.

Islamism has been described as "activist" or "political Islam".