The Lesser Sunda Islands, also known as Nusa Tenggara Islands, are an archipelago in Maritime Southeast Asia. Most of the Lesser Sunda Islands are located within the Wallacea region, except for the Bali province which is west of the Wallace Line and is within the Sunda Shelf. Together with the Greater Sunda Islands to the west they make up the Sunda Islands. The islands are part of a volcanic arc, the Sunda Arc, formed by subduction along the Sunda Trench in the Java Sea. Slightly over 20 million people live on the islands. Etymologically, Nusa Tenggara means "Southeast Islands" from the words of nusa which means 'island' from Old Javanese language and tenggara means 'southeast'.

The Sunda Trench, earlier known as and sometimes still indicated as the Java Trench, is an oceanic trench located in the Indian Ocean near Sumatra, formed where the Australian-Capricorn plates subduct under a part of the Eurasian Plate. It is 3,200 kilometres (2,000 mi) long with a maximum depth of 7,290 metres. Its maximum depth is the deepest point in the Indian Ocean. The trench stretches from the Lesser Sunda Islands past Java, around the southern coast of Sumatra to the Andaman Islands, and forms the boundary between the Indo-Australian Plate and Eurasian Plate. The trench is considered to be part of the alpida Belt as well as one of oceanic trenches around the northern edges of the Australian Plate.