Riau (Jawi: رياو) is a province of Indonesia. It is located on the central eastern coast of the island of Sumatra, and extends from the eastern slopes of the Barisan Mountains to the Malacca Strait, including several large islands situated within the Strait. The province shares land borders with North Sumatra to the northwest, West Sumatra to the west, and Jambi to the south, and a maritime border with the Riau Islands and the country of Malaysia to the east. It is the second-largest province in the island of Sumatra after South Sumatra with a total land area of 93,356.32 km², and an estimated population of 7,007,353 in 2024. The province comprises ten regencies and two cities, with Pekanbaru serving as the capital and largest city.
Historically, Riau has been a part of various monarchies before the arrival of European colonial powers. Muara Takus, a Buddhist temple complex believed to be a remnant of the Buddhist empire of Srivijaya c. 11th-12th century, is situated in Kampar Regency in Riau province. Following the spread of Islam in the 14th century, the region was then under control of Malay sultanates of Siak Sri Indrapura, Indragiri, and Johor. The sultanates later became protectorate of the Dutch and were reduced to puppet states of the Dutch East Indies. After the establishment of Indonesia in 1945, Riau belonged to the republic's provinces of Sumatra (1945–1948) and Central Sumatra (1948–1957). On 10 August 1957, the province of Riau was inaugurated and it included the Riau Islands until 2004.