ProQuest Dissertations and Theses 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. PQDT — Full Text includes millions of searchable citations to dissertation and theses from around the world from 1861 to the present day together with over a million full text dissertations that are available for download in PDF format. Over 2.1 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.