The Unity of the Brethren (Czech: Jednota bratrská; Latin: Unitas Fratrum), also known as the Czech or Bohemian Brethren, is a Protestant Christian denomination whose roots are in the pre-Reformation work of Petr Chelčický and the priest and philosopher Jan Hus, who was martyred in 1415.
The reforms of Jan Hus, which included providing the Scriptures to the people in their own language and making both elements of communion available to the people, were popular with the Czech people, but met extreme opposition from church authorities. Hus was executed, but his preaching and writings were instrumental in the formation of the Hussite movement. The Hussite movement broke into several strands, one of which (the smallest) became known as the Unity of the Brethren.
The roots of this radical and pacifistic stream within the early Hussite movement go back to Petr Chelčický. Official formation is usually attributed to the year 1457 when the first ordinations took place in a small village called Kunvald near Žamberk and Litice, which was under the lordship of King George Podiebrad, in northeastern Bohemia. The original theological foundation for the future Unity of the Brethren was laid by Petr Chelčický and Brother Řehoř (Gregor), the latter often considered one of the main founders. Lukáš Pražský, whose theological ideas strongly shaped the movement after the passing of Chelčický and Řehoř, provided later leadership. Another important leader was Jan Augusta, who spent many years in horrible imprisonment. The "last bishop" of Unity of the Brethren, Comenius (Jan Amos Komenský) is known for his reforms in education. During the second half of the 16th century, members of the Unity of the Brethren translated the Bible from the original languages into the Czech. This translation is known as the Bible of Kralice (Bible kralická), which until recently the most widely used Czech biblical translation, with an influence similar to the King James Version in the English-speaking world.