Horatio Parker (September 15, 1863–December 18, 1919) was an American composer and teacher. He was a central figure in musical life in New Haven, Connecticut in the late 19th century, and is also remembered as the teacher of Charles Ives.

He was born in Auburndale, Massachusetts. After early study in the United States with George Whitefield Chadwick and others, he went to Europe, a common destination for a young American composer in the 1880s. In Munich he studied with Josef Rheinberger; also in Munich he composed his first significant works, including a symphony and a dramatic cantata. After returning to the U.S. he took a succession of jobs as a teacher, organist and choirmaster, mostly in New York City. In 1893 he became professor at Yale University, a position which he held for the rest of his life.

While Parker is mostly remembered for a single work, the oratorio Hora novissima, he was a prolific and versatile composer in a mostly conservative Germanic tradition, writing two operas, songs, organ music, incidental music, and a copious quantity of music for chorus and orchestra. Influences in his music include Mendelssohn, Brahms, Wagner, as well as Debussy and Elgar in some works which he composed closer to 1900. During his lifetime he was considered to be the finest composer in the United States, a superior craftsman writing in the most advanced style.