Black Hand, or Crna Ruka (Црна Рука), officially Ujedinjenje ili Smrt (Ујединјеје или Смрт) ("Unification or Death") was a secret association founded in Serbia by pan-Serbian nationalists in May 1911 with the intention of uniting all of the territories containing Serb populations (notably Bosnia and Herzegovina, annexed by Austria-Hungary in October 1908). The society's implication in the June 1914 assassination in Sarajevo of Franz Ferdinand, Archduke of Austria helped spark World War I.

The group encompassed a range of ideological outlooks, from conspiratorially-minded army officers to idealistic youths, sometimes tending towards republicanism despite the acquiescence of nationalistic royal circles in its activities (the movement's leader, Col. Dragutin Dimitrijević or "Apis", had been instrumental in the June 1903 coup which had brought King Petar Karađorđević to the Serbian throne following 45 years of rule by the rival Obrenović dynasty).

In May 1917 Dimitrijević was tried on charges of plotting against the royal government, then exiled in Thessaloniki, Greece following Serbia's occupation by Austro-Hungarian, German and Bulgarian forces in late 1915. His subsequent execution signalled the Black Hand's eclipse by the monarchist White Hand, which was to dominate the political outlook of military leaders in the inter-war Yugoslav kingdom.