Borneo is the third largest non-continental island in the world (after Greenland and New Guinea). The island is located in Southeast Asia, straddling the equator. It's sparsely populated and famous for ancient rainforests filled with wildlife, including several primates and various rare and endangered species. The island also has extensive caves and rivers. In Indonesian, the term Kalimantan is used to refer to the entire island of Borneo, not just the Indonesian-controlled part as in Malay and English.

It is divided into three parts, administered by separate countries:

Brunei a tiny oil-rich monarchy occupying two small portions of the northwestern coast

East Malaysia (Sabah and Sarawak) the Malaysian part, occupying the northern third of the island

Kalimantan (Central, East, South and West) the Indonesian part, occupying the central and southern regions

Some islands that are part of the Philippines — Palawan and the Sulu Islands — are geographically close to Sabah, and have some things in common with Borneo in flora, fauna, history and culture.

The island's main airports by passenger traffic are Pontianak (PNK ^IATA), Banjarmasin (BDJ ^IATA), and Balikpapan (BPN ^IATA) in Indonesia and Kota Kinabalu (BKI ^IATA) and Kuching (KCH ^IATA) in Malaysia.