Terra nullius () adalah istilah dalam bahasa Latin yang berasal dari hukum Romawi, yang berarti "tanah tak bertuan". Istilah ini digunakan pada hukum internasional untuk wilayah tanpa kepemilikan dari suatu negara. Wilayah terra nullius dapat dikuasai oleh suatu negara melalui pendudukan.<ref>{{cite web 
  | author =
  | title = New Jersey v. New York, 523 US 767 (1998)
  | publisher = US Supreme Court
  | url = http://openjurist.org/523/us/767/new-jersey-v-new-york
  | date = 26-05-1998
  | accessdate = 29-01-2010 
  | quote = Even as to terra nullius, like a volcanic island or territory abandoned by its former sovereign, a claimant by right as against all others has more to do than planting a flag or rearing a monument. Since the 19th century the most generous settled view has been that discovery accompanied by symbolic acts give no more than "an inchoate title, an option, as against other states, to consolidate the first steps by proceeding to effective occupation within a reasonable time.8 I. Brownlie, Principles of Public International Law 146 (4th ed.1990); see also 1 C. Hyde, International Law 329 (rev.2d ed.1945); 1 L. Oppenheim International Law §§222-223, pp. 439-441 (H. Lauterpacht 5th ed.1937); Hall A Treatise on International Law, at 102-103; 1 J. Moore, International Law 258 (1906); R. Phillimore, International Law 273 (2d ed. 1871); E. Vattel, Law of Nations, §208, p. 99 (J. Chitty 6th Am. ed. 1844). 
}}</ref>
Contoh terra nullius yang ada kini adalah:
 Wilayah Bir Tawil antara Mesir dan Sudan
 Marie Byrd Land'' di Antartika
 Perairan internasional
 Objek-objek di luar angkasa seperti Bulan

Catatan kaki

Pranala luar 
 A History of the concept of "Terra Nullius" The University of Sydney 
 Governor Burke's 1835 Proclamation of terra nullius  NSW Migration Heritage Centre - Statement of Significance
 Veracini L, An analysis of Michael Conner's denial of terra nullius (The Invention of Terra Nullius)

Hukum internasional