ProQuest Dissertations & Theses Global (PQDT Global) database is the world's most comprehensive collection of multidisciplinary dissertations and theses, featuring 6 million records from more than 70 countries and over 4,100 institutions, of which 4 million are full-text titles. 
PQDT Global adds more than 300,000 new full-text dissertations each year and has metadata from 1637 to the present and full text from 1997 to the present, with select older titles. 

More information can be found on the ProQuest information portal.