Jan Hus (; Czech: [ˈjan ˈɦus] (listen); c. 1372 – 6 July 1415), sometimes anglicized as John Hus or John Huss, and referred to in historical texts as Iohannes Hus or Johannes Huss, was a Czech theologian and philosopher who became a Church reformer and the inspiration of Hussitism, a key predecessor to Protestantism, and a seminal figure in the Bohemian Reformation. Hus is considered by some to be the first Church reformer, even though some designate this honour to the theorist John Wycliffe or Marcion of Sinope. His teachings had a strong influence, most immediately in the approval of a reformed Bohemian religious denomination and, over a century later, on Martin Luther. Hus was a master, dean, and rector at the Charles University in Prague 1409-1410.

Jan Hus was born in Husinec, Bohemia to poor parents. In order to escape poverty, Hus trained for the priesthood. At an early age he traveled to Prague, where he supported himself by singing and serving in churches. His conduct was positive and, reportedly, his commitment to his studies was remarkable. After earning a Bachelor of Arts degree and being ordained as a priest, Hus began to preach in Prague. He opposed many aspects of the Catholic Church in Bohemia, such as their views on ecclesiology, simony, the Eucharist, and other theological topics.

When Alexander V was elected as a pope, he was persuaded to side with Bohemian Church authorities against Hus and his disciples. He issued a Papal bull that excommunicated Hus; however, it was not enforced, and Hus continued to preach. Hus then spoke out against Alexander V's successor, Antipope John XXIII, for his selling of indulgences. Hus' excommunication was then enforced, and he spent the next two years living in exile. When the Council of Constance assembled, Hus was asked to be there and present his views on the dissension within the Church. When he arrived, he was immediately arrested and put in prison. He was eventually taken in front of the council and asked to recant his views. He replied, "I would not for a chapel of gold retreat from the truth!". When he refused, he was put back in prison. On 6 July 1415, he was burned at the stake for heresy against the doctrines of the Catholic Church. He could be heard singing Psalms as he was burning. Among his dying words, Hus predicted that God would raise others whose calls for reform would not be suppressed; this was later taken as a prophecy about Martin Luther (born 68 years after Hus's death).

After Hus was executed, the followers of his religious teachings (known as Hussites) refused to elect another Catholic monarch and defeated five consecutive papal crusades between 1420 and 1431 in what became known as the Hussite Wars. Both the Bohemian and the Moravian populations remained majority Hussite until the 1620s, when a Protestant defeat in the Battle of the White Mountain resulted in the Lands of the Bohemian Crown coming under Habsburg dominion for the next 300 years and being subject to immediate and forced conversion in an intense campaign of return to Catholicism.