In the American wind band, the role of the horn has transformed parallel to the development of professional bands, military bands, and collegiate wind ensembles. An incomplete definition of the horn's role is discussed in various writings from 1912 to1988. With a brief history of the Sousa and Goldman Bands, collegiate wind ensembles, and commissions of United States military bands, current definitions of the horn's many roles in band music are determined. Horn parts in the works of Sousa, Holst, Vaughan Williams, Grainger, Gould, Persichetti, Hanson, Reed, Jenkins, Williams, McBeth, Husa, Hindemith, Knox, Smith, Schuller, Nixon, and Barnes, are considered for their scoring, function, technique, and virtuosity. These examples constitute a representative sample of horn parts depicting the evolution of the horn's role from rhythmic punctuation to featured melodic line. The horn's range and various techniques are discussed as well.