prolific U.S. composer of orchestral works, modern dance and film scores, and teaching pieces and choral arrangements.

Riegger moved with his family first to Indianapolis, Ind., and then at age 15 to New York City. In 1900 he began playing cello in the family ensemble. He studied music theory with the noted teacher Percy Goetschius at the Institute of Musical Art (graduated 1907) and later in Germany with the composer Max Bruch at the Berlin Hochschule für Ausübende Tonkunst.

He conducted opera in Germany (1915–17), returning to the United States to teach at Drake University, Des Moines, Iowa (1918–22). His earliest works survive from this period, conservative, lush scores that won him the Paderewski Prize (1921). From 1924 he taught in New York City; in that year he won the E.S. Coolidge Award for La Belle dame sans merci (to the poem by Keats), a score for four solo voices and chamber orchestra. His Study in Sonority (1927) for 10 violins, or any multiple of 10, marked a transition toward a dissonant, contrapuntal style. He then became an early U.S. adaptator of 12-tone technique in Dichotomy (1932), based on his study of Arnold Schoenberg's music.

Riegger's free use of the 12-tone style is expressive and lyrical at the same time that it is technically advanced. His Third Symphony (1948), which combines 12-tone and conventional writing, brought him wide attention. His later works use strict forms such as canon and fugue and incorporate traditional with experimental material (Variations for violin and orchestra, Quintuple Jazz, both 1959).