West Sumba Regency is a regency in East Nusa Tenggara Province of Indonesia. Established in 1958, the regency was considerably reduced on 2 January 2007 with the creation of new Regencies on Sumba Island under Law UU No.16 of that year. Its area is now 737.42 km2, and its population was 110,993 at the 2010 census and 145,097 at the 2020 Census; the official estimate as at mid 2023 was 152,414. It has its seat (capital) in (Kota) Waikabubak.

East Nusa Tenggara is the southernmost province of Indonesia. It comprises the eastern portion of the Lesser Sunda Islands, facing the Indian Ocean in the south and the Flores Sea in the north. It consists of more than 500 islands, with the largest ones being Sumba, Flores, and the western part of Timor; the latter shares a land border with the separate nation of East Timor. The province is subdivided into twenty-one regencies and the regency-level city of Kupang, which is the capital and largest city.