Aceh ( (listen) AH-cheh), officially the Aceh Province (Indonesian: Provinsi Aceh, Jawi: اچيه), is the westernmost province of Indonesia. It is located on the northernmost of Sumatra island, with Banda Aceh being its capital and largest city. Granted a special autonomous status, Aceh is a religiously conservative territory and the only Indonesian province practicing the Sharia law officially. There are ten indigenous ethnic groups in this region, the largest being the Acehnese people, accounting for approximately 80% to 90% of the region's population.

Aceh is where the spread of Islam in Indonesia began, and was a key factor of the spread of Islam in Southeast Asia. Islam reached Aceh (Kingdoms of Fansur and Lamuri) around 1250 AD. In the early 17th 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 resistance to control by outsiders, including the former Dutch colonists and later the Indonesian government.

Aceh has substantial natural resources of oil and natural gas. Aceh was the closest point of land to the epicenter of the 2004 Indian Ocean earthquake and tsunami, which devastated much of the western coast of the province. Approximately 170,000 Indonesians were killed or went missing in the disaster. The disaster helped precipitate the peace agreement between the government of Indonesia and the terrorist-separatist group of Free Aceh Movement.