An Islamic state is a state that has a form of government based on Islamic law (sharia). As a term, it has been used to describe various historical polities and theories of governance in the Islamic world. As a translation of the Arabic term dawlah islāmiyyah (Arabic: دولة إسلامية) it refers to a modern notion associated with political Islam (Islamism). Notable examples of historical Islamic states include the State of Medina, established by the Islamic prophet Muhammad, and the Arab Caliphate which continued under his successors and the Umayyads.

The concept of the modern Islamic state has been articulated and promoted by ideologues such as Sayyid Rashid Rida, Mohammed Omar, Abul A'la Maududi, Ayatollah Ruhollah Khomeini, Israr Ahmed, Sayyid Qutb and Hassan al-Banna. Implementation of Islamic law plays an important role in modern theories of the Islamic state, as it did in classical Islamic political theories. However, most of the modern theories also make use of notions that did not exist before the modern era.

Today, many Muslim countries have incorporated Islamic law, wholly or in part, into their legal systems. Certain Muslim states have declared Islam to be their state religion in their constitutions, but do not apply Islamic law in their courts. Islamic states that are not Islamic monarchies are mostly Islamic republics.