Barbara Zápolya (Hungarian: Szapolyai Borbála, Lithuanian: Barbora Zapojajietė, 1495–1515) was Queen of Poland and Grand Duchess of Lithuania as the first wife of King-Grand Duke Sigismund I the Old from 1512 to 1515.

Marriage to Barbara represented an alliance between Sigismund and the House of Zápolya against the Habsburgs in succession disputes over the throne to the Kingdom of Hungary.

She was the daughter of Stephen Zápolya, Palatine of Hungary and Count of Szepes, and the Polish princess Hedwig of Cieszyn of the Piast dynasty.

Not having any inheritance in either Poland or Lithuania, he lived in Buda, at the court of his elder brother King Vladislaus II of Hungary, in 1498–1501 and 1502–1506.

Sigismund was elected as King of Poland and Grand Duke of Lithuania and faced growing ambitions of the Habsburgs not only in Hungary and Bohemia, but also in the State of the Teutonic Order in Prussia.

[4] Before deciding on Barbara, Sigismund also considered Catherine of Mecklenburg, but that plan was interrupted by renewed hostilities between Poland and Bogdan III the One-Eyed, Voivode of Moldavia.

[4] Tomicki informed King Vladislaus that his brother sought to wed a Hungarian noblewoman and asked for his assistance in locating a suitable candidate.

Barbara, escorted by her family and Polish nobles (Bishop Jan Lubrański, Krzysztof Szydłowiecki, Andrzej Krzycki), departed to Poland in January 1512.

[7] Maximilian I, Holy Roman Emperor, attempted to interrupt the wedding with a last-minute proposal for Sigismund to marry one of the daughters of Francesco II Gonzaga, Marquess of Mantua.

[7] In exchange for the dowry, Barbara received the towns of Nowy Korczyn, Wiślica, Żarnowiec, Radom, Jedlnia, Kozienice, Chęciny, Stężyca, and others as well as income from custom taxes of several cities and an annual sum of 200 Hungarian florins from the Wieliczka Salt Mine.

[11] Marcin Kromer even attributed the victory at Orsha to her Catholic piety and devotion, while Justus Ludwik Decjusz did not doubt that Barbara would join ranks of saints in the heaven.

For example, her mother and brother urged her to prevent Piotr Tomicki, a known sympathizer with the Habsburgs, from becoming Bishop of Przemyśl and Vice-Chancellor of the Crown.

[12] Marriage to Barbara also did not stop Sigismund from supporting the wedding between Louis II of Hungary and Maria of Austria, granddaughter of Maximilian I, Holy Roman Emperor.