Jadwiga (Polish: [jadˈviɡa] (listen); 1373 or 1374 – 17 July 1399), also known as Hedwig (Hungarian: Hedvig), was the first female monarch of the Kingdom of Poland, reigning from 16 October 1384 until her death. She was the youngest daughter of Louis the Great, King of Hungary and Poland, and his wife Elizabeth of Bosnia. Jadwiga was a member of the Capetian House of Anjou, but she had more close forebears among the Polish Piasts than among the Angevins. In 1997 she was canonized by the Catholic Church.

In 1375 it was planned that she would eventually marry William of Austria, and would live in Vienna from 1378 to 1380. Jadwiga's father is thought to have regarded her and William as his favoured successors in Hungary after the 1379 death of her eldest sister, Catherine, since the Polish nobility had that same year pledged their homage to Louis' second daughter, Mary, and Mary's fiancé, Sigismund of Luxembourg. However, Louis died, and in 1382, at her mother's insistence, Mary was crowned "King of Hungary". Sigismund of Luxembourg tried to take control of Poland, but the Polish nobility countered that they would be obedient to a daughter of King Louis only if she settled in Poland. Queen Elizabeth then chose Jadwiga to reign there, but did not send her to Kraków to be crowned. During the interregnum, Siemowit IV, Duke of Masovia, became a candidate for the Polish throne. The nobility of Greater Poland favored him and proposed that he marry Jadwiga. However, Lesser Poland's nobility opposed him and persuaded Queen Elizabeth to send Jadwiga to Poland.

Jadwiga was crowned king in Poland's capital, Kraków, on 16 October 1384. Her coronation either reflected the Polish nobility's opposition to her intended husband, William, becoming king without further negotiation, or simply emphasized her status as queen regnant. With her mother's consent, Jadwiga's advisors opened negotiations with Jogaila, Grand Duke of Lithuania, who was still a pagan, concerning his potential marriage to Jadwiga. Jogaila signed the Union of Krewo, pledging to convert to Catholicism and to promote his pagan subjects' conversion. Meanwhile, William hastened to Kraków, hoping to marry his childhood fiancé Jadwiga, but in late August 1385 the Polish nobles expelled him. Jogaila, who took the baptismal name Władysław, married Jadwiga on 15 February 1386. Legend says that she had agreed to marrying him only after lengthy prayer, seeking divine inspiration.

Jogaila, now in Polish styled Władysław Jagiełło, was crowned King of Poland on 4 March 1386. As Jadwiga's co-ruler, Jagiełło worked closely with his wife. After rebellious nobles of the Kingdom of Hungary-Croatia had imprisoned her mother and sister, she marched into the Kingdom of Galicia–Volhynia, which had been under Hungarian rule, and persuaded most of the inhabitants to become subjects of the Polish Crown. She mediated between her husband's quarreling kin, and between Poland and the Teutonic Knights. After her sister Mary died in 1395, Jadwiga and Jagiełło laid claim to Hungary against the widowed Sigismund of Luxembourg, but the Hungarian lords failed to support them.