Aceh (/ˈɑːtʃeɪ/; [ʔaˈtɕɛh]) is a special region (Indonesian: daerah istimewa) of Indonesia, located on the northern tip of the island of Sumatra. Its first full name, Aceh Darussalam (1511–1959) then, Daerah Istimewa Aceh (1959–2001), Nanggroë Aceh Darussalam (2001–2009) and Aceh (2009–Present). Past spellings of its name include Acheh, Atjeh and Achin. The Aceh province has the highest proportion of Muslims in the country with regional levels of Sharia law.

It is thought to have been in Aceh where Islam was first established in Southeast Asia. In the early seventeenth century the Sultanate of Aceh was the most wealthy, powerful and cultivated state in the Malacca Straits region. Aceh has a history of political independence and fierce resistance to control by outsiders, including the former Dutch colonists and the Indonesian government. Aceh has substantial natural resources, including oil and natural gas—some estimates put Aceh gas reserves as being the largest in the world. Relative to most of Indonesia, it is a religiously conservative area.