Brundibár is a children's opera by Jewish Czech composer Hans Krása with a libretto by Adolf Hoffmeister, originally performed by the children of Theresienstadt concentration camp in occupied Czechoslovakia. The name comes from a Czech colloquialism for a bumblebee.

Krása and Hoffmeister wrote the opera in 1938 for a government competition, but the competition was later cancelled due to political developments. Rehearsals started in 1941 at the Jewish orphanage in Prague, which served as a temporary educational facility for children separated from their parents by the war. In the winter of 1942 the opera was first performed at the orphanage: by this time, composer Krása and set designer František Zelenka had already been transported to Theresienstadt. By July 1943, nearly all of the children of the original chorus and the orphanage staff had also been transported to Theresienstadt. Only the librettist Hoffmeister was able to escape Prague in time.

Reunited with the cast in Theresienstadt, Krása reconstructed the full score of the opera, based on memory and the partial piano score that remained in his hands, adapting it to suit the musical instruments available in the camp: flute, clarinet, guitar, accordion, piano, percussion, four violins, a cello and a double bass. A set was once again designed by František Zelenka, formerly a stage manager at the Czech National Theatre: several flats were painted as a background, in the foreground was a fence with drawings of the cat, dog and lark and holes for the singers to insert their heads in place of the animals' heads. On 23 September 1943, Brundibár premiered in Theresienstadt. The production was directed by Zelenka and choreographed by Camilla Rosenbaum, and was shown 55 times in the following year.

A special performance of Brundibár was staged in 1944 for representatives of the Red Cross who came to inspect living conditions in the camp; what the Red Cross did not know at the time was that much of what they saw during their visit was a show, and that one of the reasons the Theresienstadt camp seemed comfortable was that many of the residents had been deported to Auschwitz in order to reduce crowding during their visit.

Later that year this Brundibár production was filmed for a Nazi propaganda film Der Führer schenkt den Juden eine Stadt (The Führer Gives the Jews a City). All of the participants in the Theresienstadt production were herded into cattle trucks and sent to Auschwitz as soon as filming was finished. Most were gassed immediately upon arrival, including the children, the composer Krása, the director Kurt Gerron, and the musicians.

The Brundibár footage from the film is included in the Emmy Award-winning documentary Voices of the Children directed by Zuzana Justman, a Terezin survivor, who sang in the chorus. Ela Weissberger, who played the part of the cat, appears in the film. The footage appears again in As Seen Through These Eyes, a 2009 documentary directed by Hilary Helstein. There Weissberger describes the opera in some detail, noting that the only time that the children were permitted to remove their yellow stars was during a performance.