Banjarmasin is the largest city in South Kalimantan, Indonesia. It was the capital of the province until 15 February 2022. The city is located on a delta island near the confluence of the Barito and Martapura rivers. Historically the centre of the Banjarese culture, and the capital of the Sultanate of Banjar, it is the biggest city in South Kalimantan and one of the main cities of Kalimantan. The city covers an area of 98.37 km² (37.98 sq mi) and had a population of 625,481 as of the 2010 Census and 657,663 as of the 2020 Census; the official estimate as of mid 2024 was 681,693 (comprising 341,066 males and 340,627 females). It is the third most populous city on the island of Borneo.

Greater Banjarmasin, also known as Banjarbakula (an acronym for Banjarmasin-Barito Kuala-Tanah Laut) or Banjar Raya, is an urban agglomeration of over two million people covering an area of 6,737.70 km² (2,601.44 sq mi), which includes Banjarbaru city and parts of Banjar Regency (including Martapura town), Barito Kuala Regency, and Tanah Laut Regency, and accounts for 2,076,771 inhabitants in mid 2024, amounting to almost half of the province's population.

Banjarmasin was the de jure seat of the South Kalimantan governor and the location of the provincial parliament, although some provincial buildings have been relocated to Banjarbaru. On 15 February 2022, the capital of South Kalimantan province was legally moved to Banjarbaru.

Negara Dipa (1380–1478)
Negara Daha (1478–1520)
Banjar Sultanate (1520–1526)
Demak Sultanate (1526–1546)
Banjar Sultanate (1546–1621)
Kingdom of Denmark (1621–1636)
VOC (1636–1638)
Banjar Sultanate (1638–1701)
England (1701–1707)
Banjar Sultanate (1707–1787)
Dutch Republic (1787–1795)
Batavian Republic (1795–1806)
Dutch East Indies (1806–1809)
Banjar Sultanate (1809–1815)
Kingdom of Great Britain and Ireland (1815–1816)
Dutch East Indies (1817–1942)
Empire of Japan (1942–1945)
Dutch East Indies (1945–1949)
Indonesia (1949–today)

"Banjarmasin" is thought to be a corrupted version of "Bandar Masih" (Port Masih), which was named for Patih Masih, who ruled the port and the surrounding villages. Patih Masih's name may have been a nickname. Masih originates from the Ngaju language. Oloh Masi refers to the coastal-dwelling Malay population in the language of the Dayaks, who lived in the interior and visited the port regularly to trade. Some of the Dayaks eventually settled in the port. They eventually contributed to the culture of the Banjar people, along with the Javanese and Malays.

European archeologist H. Kupper discovered several prehistoric sites around the region in 1939 and found implements such as choppers and other stone tools. Most of the artifacts found around the region and the province show signs of Neolithic culture. Migration from mainland Asia to Borneo may have been common while they were connected by the Sunda Shelf. Many stone tools have been found in Awang Bangkal, 50 km (31 mi) from the city.

Until the early 15th century, there were few written records found from the region. Outside records indicate it was home to several kingdoms such as Tanjungpuri—theorized to have been founded by Malay people from Srivijaya—and Negara Daha and Dipa, which were founded by Javanese people from Majapahit. Hinduism and Buddhism entered the region between the first and 15th centuries. There are two candis (temples) left in the region, Candi Laras and Candi Agung. The Ma'anyan people may have ruled the oldest kingdom in the archipelago, Nan Sarunai. Its existence is disputed; speculated by archeologists based on several carved stone tombs and a Ma'anyan folk song called "Usak Jawa", which is thought to tell the story of the Majapahit conquest of the kingdom.

The history of Banjarmasin itself began during the founding of the Sultanate of Banjar. According to folk stories and the Hikayat Banjar, Sukarama, the fourth king of Negara Daha, wanted his grandson, Raden Samudra, to be his successor in the kingdom instead of his direct son Prince Tumenggung. Prince Tumenggung later banished Raden Samudra and tried to reclaim the throne for himself. Raden Samudra fled to the region that would later be known as Banjarmasin. There, he met Patih Masih. Under Samudra's leadership, the port grew into the town of Bandar Masih. Tumenggung, who disliked Samudra's growing power, wanted to invade the town. Samudra allied with the Demak Sultanate, which agreed to help him. In return he would have to convert to Islam if he won. With the help of expeditionary forces from Demak, Samudra defeated the Tumenggung forces and proclaimed the Banjar Sultanate. He changed his name to Sultan Suriansyah I. The sultanate became more reliant on the Demak to the point that it was considered their protectorate. However, between 1546 and 1550, as conquests and the spice trade enriched the sultanate, it became independent and stopped sending tributes to Java.