Charles Edward Ives (/aɪvz/; October 20, 1874 – May 19, 1954) was an American modernist composer, actuary and businessman. Ives was among the earliest renowned American composers to achieve recognition on a global scale. His music was largely ignored during his early career, and many of his works went unperformed for many years. Later in life, the quality of his music was publicly recognized through the efforts of contemporaries like Henry Cowell and Lou Harrison, and he came to be regarded as an "American original".

Ives was also among the first composers to engage in a systematic program of experimental music, with musical techniques including polytonality, polyrhythm, tone clusters, aleatory elements, and quarter tones. The experimentation foreshadowed many musical innovations that were later more widely adopted during the 20th century; hence, Ives is often regarded as the leading American composer of art music of the 20th century.

Sources of Ives's tonal imagery included hymn tunes and traditional songs; he also incorporated melodies of town bands at holiday parades, the fiddlers at Saturday night dances, patriotic songs, sentimental parlor ballads, and the melodies of Stephen Foster.

Ives was born in Danbury, Connecticut, on October 20, 1874, the son of George (Edward) Ives, a US Army bandleader in the American Civil War, and his wife, Mary Elizabeth Ives. The Iveses, descended from founding colonists of Connecticut, were one of Danbury's leading families, and they were prominent in business and civic improvement. They were similarly active in progressive social movements of the 19th century, including the abolition of slavery.

George Ives directed bands, choirs, and orchestras, and taught music theory and a number of instruments. Charles got his influences by sitting in the Danbury town square and listening to his father's marching band and other bands on other sides of the square simultaneously. His father taught him and his brother (Joseph) Moss Ives (February 5, 1876 – April 7, 1939) music, teaching harmony and counterpoint and guided his first compositions; George took an open-minded approach to theory, encouraging him to experiment in bitonal and polytonal harmonizations. It was from him that Ives also learned the music of Stephen Foster. He became a church organist at the age of 14 and wrote various hymns and songs for church services, including his Variations on "America", which he wrote for a Fourth of July concert in Brewster, New York. It is considered challenging even by modern concert organists, but he famously spoke of it as being "as much fun as playing baseball", a commentary on his own organ technique at that age.

Ives moved to New Haven, Connecticut, in 1893, enrolling in the Hopkins School, where he captained the baseball team. In September 1894, Ives entered Yale University, studying under Horatio Parker. Here he composed in a choral style similar to his mentor, writing church music and even an 1896 campaign song for William McKinley. On November 4, 1894, his father died, a crushing blow to him, but to a large degree, he continued the musical experimentation he had begun with him. His brother Moss later became a lawyer.

At Yale, Ives was a prominent figure; he was a member of HeBoule, Delta Kappa Epsilon (Phi chapter) and Wolf's Head Society, and sat as chairman of the Ivy Committee. He enjoyed sports at Yale and played on the varsity American football team. Michael C. Murphy, his coach, once remarked that it was a "crying shame" that he spent so much time at music as otherwise he could have been a champion sprinter. His works Calcium Light Night and Yale-Princeton Football Game show the influence of college and sports on Ives's composition. He wrote his Symphony No. 1 as his senior thesis under Parker's supervision. Ives continued his work as a church organist until May 1902.

Soon after he graduated from Yale in 1898, he started work in the actuarial department of the Mutual Life Insurance Company of New York. In 1899, Ives moved to employment with the insurance agency Charles H. Raymond & Co., where he stayed until 1906. In 1907, upon the failure of Raymond & Co., he and his friend Julian Myrick formed their own insurance agency Ives & Co., which later became Ives & Myrick, where he remained until he retired.