The aim of this paper is to investigate how contemporary music composition aesthetics and performance practices in orchestral music came to be defined and institutionalized in New York City through the 1960s and 1970s. The geographic distinctions commonly referred to as Uptown and Downtown identify separate networks of American contemporary music that sprouted in New York City already in the 1950s, and developed across the United States in the second half of the twentieth century. I propose that the division of contemporary music practices and the ultimate institutionalization of Uptown is inextricably linked to changing orchestral practices in New York City in the late 1960s and 1970s.   Using the digital program archives from the New York Philharmonic and Carnegie Hall, I analysed contemporary programming in orchestral and large ensemble concerts from 1960 to 1975. Using this data, one observes that contemporary music programming decreased in this period, that the performance of contemporary music became less stylistically diverse, and that “contemporary music”, as a genre, came to be increasingly defined as European and modernist. I therefore conclude that changing orchestral practice was a major contributing factor in the division and institutionalization of contemporary musical practices in New York City.