Jihad (; Arabic: جهاد, romanized: jihād [dʒiˈhaːd]) is an Arabic word which literally means "striving" or "struggling", especially with a praiseworthy aim. In an Islamic context, it can refer to almost any effort to make personal and social life conform with God's guidance, such as struggle against one's evil inclinations, proselytizing, or efforts toward the moral betterment of the Muslim community (Ummah), though it is most frequently associated with war. In classical Islamic law (sharia), the term refers to armed struggle against unbelievers, while modernist Islamic scholars generally equate military jihad with defensive warfare. In Sufi circles, spiritual and moral jihad has been traditionally emphasized under the name of greater jihad. The term has gained additional attention in recent decades through its use by various insurgent Islamic extremist, militant Islamist, and terrorist individuals and organizations whose ideology is based on the Islamic notion of jihad.

The word jihad appears frequently in the Qur'an with and without military connotations, often in the idiomatic expression "striving in the path of God (al-jihad fi sabil Allah)", conveying a sense of self-exertion. They developed an elaborate set of rules pertaining to jihad, including prohibitions on harming those who are not engaged in combat. In the modern era, the notion of jihad has lost its jurisprudential relevance and instead given rise to an ideological and political discourse. While modernist Islamic scholars have emphasized the defensive and non-military aspects of jihad, some Islamists have advanced aggressive interpretations that go beyond the classical theory.

Jihad is classified into inner ("greater") jihad, which involves a struggle against one's own base impulses, and external ("lesser") jihad, which is further subdivided into jihad of the pen/tongue (debate or persuasion) and jihad of the sword. Most Western writers consider external jihad to have primacy over inner jihad in the Islamic tradition, while much of contemporary Muslim opinion favors the opposite view. Gallup analysis of a large survey reveals considerable nuance in the conceptions of jihad held by Muslims around the world.

The sense of jihad as armed resistance was first used in the context of persecution faced by Muslims, as when Muhammad was at Mecca, when the community had two choices: emigration (hijra) or jihad. In Twelver Shi'a Islam, jihad is one of the ten Practices of the Religion. A person engaged in jihad is called a mujahid (plural: mujahideen). The term jihad is often rendered in English as "Holy War", although this translation is controversial. Today, the word jihad is often used without religious connotations, like the English crusade.