Vojin of Gacko or Vojvoda Vojin (Serbian: Војвода Војин; fl. 1322–1347) was a Serb voivode (military commander, Duke) and magnate (velikaš) that held the province of Gacko, also known as Hum (in modern Herzegovina), in ca.1322-1347, serving King Stephen Uroš III Dečanski (r. 1322–1331) and Emperor Stephen Dušan the Mighty (r. 1331-1355). He is described as one of the most important nobles (velmoža) of King Stephen, and when the King and his son Dušan entered a succession war, Vojin supported the son. Vojin plundered Dubrovnik in August 1325, and took part in the Battle of Velbazhd (1330), and the southern military campaigns of the Serbian Empire.
Vojin is the eponymous founder of the Vojinović noble family, which eventually became one of the most powerful families as provincial lords during the fall of the Serbian Empire. His sons Altoman and Vojislav were recognized as overlords of the Hum region (Herzegovina). His daughter Vojislava married nobleman Brajko Branivojević.
- Miloš, mentioned as stavioca in 1333, died young
- Altoman (d. 1359), veliki župan, married Ratoslava Mladenović (Branković)
- Vojislav (d. 25.10.1363), veliki knez
- Vojislava (also Voisava or Sela), married Brajko Branivojević