Zdeněk Fibich (Czech pronunciation: [ˈzdɛɲɛk ˈfɪbɪx], 21 December 1850 – 15 October 1900) was a Czech composer of classical music. Among his compositions are chamber works (including two string quartets, a piano trio, piano quartet and a quintet for piano, strings and winds), symphonic poems, three symphonies, at least seven operas (the most famous probably Šárka and The Bride of Messina), melodramas including the substantial trilogy Hippodamia, liturgical music including a mass - a missa brevis; and a large cycle (almost 400 pieces, from the 1890s) of piano works called Moods, Impressions, and Reminiscences. The piano cycle served as a diary of sorts of his love for a piano pupil. He was born in Všebořice (Šebořice) near Čáslav.

That Fibich is far less known than either Antonín Dvořák or Bedřich Smetana can be explained by the fact that he lived during the rise of Czech nationalism within the Habsburg Empire. And while Smetana and Dvořák gave themselves over entirely to the national cause, consciously writing Czech music with which the emerging nation strongly identified, Fibich’s position was more ambivalent. That this was so was due to the background of his parents and to his education. Fibich’s father was a Czech forestry official and the composer’s early life was spent on various wooded estates of the nobleman for whom his father worked. His mother, however, was an ethnic German Viennese. Home schooled by his mother until the age of nine, he was first sent to a German-speaking gymnasium in Vienna for two years before attending a Czech speaking gymnasium in Prague where he stayed until he was 15. After this he was sent to Leipzig where he remained for three years studying piano with Ignaz Moscheles and composition with Salomon Jadassohn and Ernst Richter. Then, after the better part of a year in Paris, Fibich concluded his studies with Vinzenz Lachner (the younger brother of Franz and Ignaz) in Mannheim. Fibich spent the next few years living with his parents back in Prague where he composed his first opera Bukovina, based on a libretto of Karel Sabina, the librettist of The Bartered Bride. At the age of 23, he married Růžena Hanušová and took up residence in the Lithuanian city of Vilnius where he had obtained a position of choirmaster. After spending two personally unhappy years there (his wife and newly born twins both died in Vilnius), he returned to Prague in 1874 and remained there until his death in 1900. In 1875 Fibich married Růžena's sister, the operatic contralto Betty Fibichová (née Hanušová), but left her in 1895 for his former student and lover Anežka Schulzová. The relationship between Schulzová and Fibich was important to him artistically, since she both wrote the libretti for all his later operas including Šárka, but also served as the inspiration for his Moods, Impressions, and Reminiscences.

Fibich was given a bi-cultural education, living, during his formative early years, in Germany, France and Austria in addition to his native Bohemia. He was fluent in German as well as Czech. In his instrumental works, Fibich generally wrote in the vein of the German romantics, first falling under the influence of Weber, Mendelssohn and Schumann and later Wagner. His early operas and close to 200 of his early songs are in German. These works along with his symphonies and chamber music won considerable praise from German critics if not from Czechs. The bulk of Fibich’s operas are in Czech, although many are based on subjects from non-Czechs such as Shakespeare, Schiller and Byron. In his chamber music, more than anywhere else, Fibich makes use of Bohemian folk melodies and dance rhythms such as the Dumka. Fibich was the first to write a Czech nationalist tone poem (Záboj, Slavoj a Luděk) which served as the inspiration for Smetana’s Má vlast. He was also the first to use the polka in a chamber work, his quartet in A.

In the years after his return to Prague in 1874, Fibich's music encountered severely negative reactions in the Prague musical community, stemming from his (and Smetana's) adherence to Richard Wagner's theories on opera. While Smetana's later career was plagued with problems for presenting Wagnerian-style music dramas in Czech before a conservative audience, Fibich's pugilistic music criticism, not to mention his overtly Wagnerian later operas, Hedy, Šárka, and Pád Arkuna, exacerbated the problem in the years after Smetana's death in 1884. Together with the music aesthetician Otakar Hostinský he was ostracized from the musical establishment at the National Theatre and Prague Conservatory, and forced to rely on his private composition studio. This studio nevertheless was well respected among students, drawing such names as Emanuel Chvála, Karel Kovařovic, Otakar Ostrčil, and Zdeněk Nejedlý, the notorious critic and subsequent politician. Much of the reception of Fibich's music in the early twentieth century is a result of these students' efforts after their teacher's death, especially in Nejedlý's highly polemical campaigns enacted in a series of monographs and articles that sought to redress what he considered to be past inequities. Although this served to bring Fibich's music to greater attention, subsequent scholarship has had to deal with the spectre of Nejedlý's intensely personal bias.

There is a Fibich Society which has organized projects such as Hudec's Thematic Catalog below, and much else.

Fibich was the original composer of the tune for "My Moonlight Madonna" for which Paul Francis Webster wrote the English lyrics. In 1933 the tune was popularly harmonized by William Scotti.