Omar Ali Saifuddien Mosque is a mosque in Bandar Seri Begawan, the capital of Brunei. It is one of the country's two masjid negara or national mosques, as well as a national landmark. It is one of the largest and oldest mosques in the country and is named after Omar Ali Saifuddien III (1914–1986), the 28th Sultan of Brunei and the father of the current monarch Sultan Hassanal Bolkiah. The mosque serves as a symbol of the Islamic faith in Brunei.

Bandar Seri Begawan is the capital and largest city of Brunei. It is officially a municipal area with an area of 100.36 square kilometres (38.75 sq mi) and an estimated population of 100,700 as of 2007. It is part of Brunei-Muara District, the smallest yet most populous district which is home to over 70 per cent of the country's population. It is the country's largest urban centre and nominally the country's only city. The capital is home to Brunei's seat of government, as well as a commercial and cultural centre. It was formerly known as Brunei Town until it was renamed in 1970 in honour of Sultan Omar Ali Saifuddien III, the 28th Sultan of Brunei and the father of the current Sultan Hassanal Bolkiah.