Humanity’s musical treasures — Beethoven piano sonatas, Schubert songs, Mozart symphonies and the like — come to life in performance. But they truly survive as black marks on a page, otherwise known as scores. Now a Web site founded five years ago by a conservatory student, then 19 years old, has made a vast expanse of this repertory available, free.

The site, the International Music Score Library Project, has trod in the footsteps of Google Books and Project Gutenberg and grown to be one of the largest sources of scores anywhere. It claims to have 85,000 scores, or parts for nearly 35,000 works, with several thousand being added every month. That is a worrisome pace for traditional music publishers, whose bread and butter comes from renting and selling scores in expensive editions backed by the latest scholarship. More than a business threat, the site has raised messy copyright issues and drawn the ire of established publishers.

The site (imslp.org) is an open-source repository that uses the Wikipedia template and philosophy, “a visual analogue of a normal library,” in the words of its founder, Edward W. Guo, the former conservatory student. Volunteers scan in scores or import them from other sources, like Beethoven House, the museum and research institute in Bonn, Germany. Other users oversee copyright issues and perform maintenance. Quality control — like catching missed pages — is also left to the public. “It’s completely crowd sourced,” Mr. Guo said.

The site has recently begun adding recordings. And through a partnership with a freelance musician in Indiana who runs a publishing business, it offers low-cost, on-demand printing of the music, often at a tiny fraction of the cost of standard editions. The prices of major publishing houses range widely depending on the number of instruments in the work or its length. A set of parts for a mainstream string quartet, for example, can run from $30 to $50.