ProQuest Dissertations and Theses Global is the world's most comprehensive collection of dissertations and theses. The official digital dissertations archive for the Library of Congress and the database of record for graduate research. It includes nearly 3 million searchable citations to dissertation and theses from around the world from 1743 to the present day together with over 1 million full-text dissertations that are available for download in PDF format. Over 2 million titles are available for purchase as printed copies. The database offers full text for most of the dissertations added since 1997 and strong retrospective full-text coverage for older graduate works. More than 80,000 new full-text dissertations and theses are added to the database each year through dissertations publishing partnerships with 700 leading academic institutions worldwide. Each dissertation published since July 1980 includes a 350-word abstract written by the author. Master's theses published since 1988 include 150-word abstracts. Simple bibliographic citations are available for dissertations dating from 1637. The fastest way to validate or identify a dissertation outside the ProQuest Dissertation database is the ProQuest/UMI Dissertation Search.
Open access repositories at many institutions are starting to ingest older dissertations and requiring new ones to be included. Be sure to search in the Registry of Open Access Repositories or the The Directory of Open Access Repositories to find what institutions include freely available, open access dissertations. You can also go directly an institution's repository like Harvard University, University of Michigan, Cornell University, or the University of California.
Index to Theses is a comprehensive listing of theses with abstracts accepted for higher degrees by universities in the United Kingdom and Ireland since 1716. It contains records for over 600,000 theses with full text access to over 50,000. The British Library offers access to over 350,000 open access theses through EThOS: Electronic Theses Online Service. Other international dissertations can be found in the Center for Research Libraries Dissertations Search. The Center for Research Libraries is a consortium of research libraries and purchases materials that any member can borrow through Interlibrary Loan. Yale is part of CRL. Also search the Directory of Open Access Repositories or the National Digital Library of Theses and Dissertations for international dissertations.