West Kalimantan (Indonesian: Kalimantan Barat) is a province of Indonesia. It is one of five Indonesian provinces comprising Kalimantan, the Indonesian part of the island of Borneo. Its capital and largest city is Pontianak. It is bordered by East Kalimantan and Central Kalimantan to the east, the Malaysian state of Sarawak to the north, and the Bangka Belitung Islands to the west and the Java Sea to the south. The province has an area of 147,037 km², and had a population of 4,395,983 at the 2010 Census and 5,414,390 at the 2020 Census; the official estimate as at mid 2023 was 5,623,328 (comprising 2,887,209 males and 2,736,119 females), and was projected to rise to 5,695,500 at mid 2024. Ethnic groups include the Dayak, Malay, Chinese, Javanese, Bugis, and Madurese. The borders of West Kalimantan roughly trace the mountain ranges surrounding the vast watershed of the Kapuas River, which drains most of the province. The province shares land borders with Central Kalimantan to the southeast, East Kalimantan to the east, and the Malaysian state of Sarawak to the north.

West Kalimantan is nicknamed "The Province of a Thousand Rivers". The nickname references the geography of the province, which features hundreds of rivers of varying size, most of which are navigable. Several major rivers are still the main route for freight to the hinterland, despite road infrastructure now reaching most districts.

Although a small part of West Kalimantan region is seawater, West Kalimantan has dozens of large and small islands (mostly uninhabited) spread along the Karimata Strait and Natuna Sea that borders the province of Riau Islands. The total population in the province, according to the 2010 census totalled 4,395,983 inhabitants and at the 2020 Census it was 5,414,390, but by mid 2023 it was officially estimated to have reached 5,623,328.

The history of West Kalimantan was dominated with Hindu and Buddhist kingdoms ruling over the region and Borneo as a whole after that this kingdoms converted into muslim sultanate.

Its modern history in 17th century. The Malays are the native Muslims of West Kalimantan and established their Sultanates of Sambas since 1609 in Sambas territory, along with Mempawah Sultanate established since 1740 ruled in between Pontianak and Sambas territory. The Mempawah Sultanate brought in workers from China at the beginning of the kingdom. The same policy followed by the Sambas Sultanate around 1750, which brought in workers from China to work in the gold mines in the area.

The high Chinese population in this province was due to a republic founded by Chinese miners called the Lanfang Republic (蘭芳共和國: Republik Lanfang), an autonomous state allied with Pontianak and Sambas Sultanate, as a sub-state of the Qing. The government of Lanfang was ended in West Kalimantan after the Dutch Invasion in 1884. ^{[citation needed]}

West Kalimantan was under Japanese occupation from 1942 to 1945, when Indonesia declared its Independence. During the Japanese occupation, more than 21,000 people in Pontianak (including sultans, men, women and children) were kidnapped, tortured and massacred by Japanese troops during the Pontianak incidents. All the Malay Sultans on Kalimantan were executed and the Malay elite was devastated by the Japanese. Most of the victims were buried in several giant wells in Mandor (88 km from Pontianak). After the end of the war, Japanese officers in Pontianak were arrested by allied troops and brought in the International Military Tribunal for the Far East.

A monument called Makam Juang Mandor was created to memorialize the event.