A dissertation is a thesis submitted as a requirement for a doctoral degree. Library catalogs often use the technical term thesis: e.g. "Thesis (Ph.D.)."
There are different types of doctoral programs in music. The most frequently encountered are
D.M.A. (Doctor of Musical Arts): a performance degree
Ed. D. (Doctor of Education)
Ph.D. (Doctor of Philosophy): musicology, ethnomusicology, theory, composition.
While D.M.A. dissertations may be particularly useful to performers, Ph.D. dissertations tend to examine the topic in greater depth and offer more extensive bibliographies.
Dissertations and Theses Full Text (ProQuest) Recommended.
This is the primary site for dissertations in all disciplines, but coverage of titles from outside the U.S. is spotty. Master's theses are included selectively. PDFs of many dissertations are available for download, but note that others are unavailable due authors' restrictions. Also, some titles have no abstract: for these references to the print editions of Dissertation Abstracts International, American Doctoral Dissertations, and Masters Abstracts indicate where the abstract may be found.
In recent years numerous universities, including Emory, have switched to electronic dissertations and theses (EDTs). This site provides access to EDTs from the various schools. Many can be downloaded free.
Coverage starts with 1967 and is international in scope. To find dissertations only, in Advanced Search enter "doctoral dissertation" in the box for publication type.
"A comprehensive listing of theses with abstracts accepted for higher degrees by universities in Great Britain and Ireland since 1716."
For a more extensive list of dissertation sources, see the Classical Music Research Guide.