Stephen V (Hungarian: V. István, Croatian: Stjepan V., Slovak: Štefan V; before 18 October 1239 – 6 August 1272, Csepel Island) was King of Hungary and Croatia between 1270 and 1272, and Duke of Styria from 1258 to 1260. He was the oldest son of King Béla IV and Maria Laskarina. King Béla had his son crowned king at the age of six and appointed him Duke of Slavonia. Still a child, Stephen married Elizabeth, a daughter of a chieftain of the Cumans whom his father settled in the Great Hungarian Plain.
King Béla appointed Stephen Duke of Transylvania in 1257 and Duke of Styria in 1258. The local noblemen in Styria, which had been annexed four years before, opposed his rule. Assisted by King Ottokar II of Bohemia, they rebelled and expelled Stephen's troops from most parts of Styria. After Ottokar II routed the united army of Stephen and his father in the Battle of Kressenbrunn on 12 July 1260, Stephen left Styria and returned to Transylvania.
Stephen forced his father to cede all the lands of the Kingdom of Hungary to the east of the Danube to him and adopted the title of junior king in 1262. In two years, a civil war broke out between father and son, because Stephen accused Béla of planning to disinherit him. They concluded a peace treaty in 1266, but confidence was never restored between them. Stephen succeeded his father, who died on 3 May 1270, without difficulties, but his sister Anna and his father's closest advisors fled to the Kingdom of Bohemia. Ottokar II invaded Hungary in the spring of 1271, but Stephen routed him. In next summer, a rebellious lord captured and imprisoned Stephen's son, Ladislaus. Shortly thereafter, Stephen unexpectedly fell ill and died.