The scores and libretti in this Virtual Collection include first and early editions and manuscript copies of music from the eighteenth and early nineteenth centuries by J.S. Bach and Bach family members, Mozart, Schubert and other composers, as well as multiple versions of nineteenth century opera scores, seminal works of musical modernism, and music of the Second Viennese School. Many, such as variant editions of nineteenth century operas and related libretti, fall into intellectually related sets that are meant to be seen and used together. As a group, they give scholars a window into the study of historical performance practice that cannot be duplicated using the holdings of any one other library.