Once you've identified a thesis, try WorldCat, Google, and Google Scholar.  If that fails, also try the website of the university where the graduate work was completed.  Search for "theses" or "ETD."  (ETD = Electronic Theses and Dissertations)

Usually the library at the university where the graduate work was completed will have a link in their catalog.

Ask for help.

If you have identified a recent thesis or dissertation, go to the granting university's library catalog.  Most universities have started to make available electronic full text and a link may be found in their catalog.  Also, in some cases, a search on the university's website for "dissertations" or "ETD" will unearth the full text.  (ETD = electronic dissertations and theses)

Unfortunately, older theses and dissertations are usually not included.

The following repositories attempt to harvest or gather data from many individual repositories.

BASE - Bielefeld Academic Search Engine
Limit to theses.  Searches academic websites.

OAIster
OAIster is a union (combined) catalog of worldwide digital resources including digital repositories (e.g. NC DOCKS) which may contain dissertations and theses. OAIster links to the full text or original material. Other forms of digitized material available are books and articles, audio files (e.g., wav, mp3), images (e.g., tiff, gif), movies (e.g., mp4, quicktime), and datasets (e.g., downloadable statistics files).

(NDLTD) Networked Digital Library of Theses and Dissertations

Provides abstracts and links to selected electronic theses and dissertations (ETDs) from universities around the world.  Access to some full-text ETD's may be restricted. This is the interface for searching this collection:  VTLS Visualizer.  (Scirus ETD Search no longer works.)

Theses Canada Portal
No new dissertations have been added since 2016.  Theses Canada Portal is the central access point for Canadian theses. At this site, you can search AMICUS, Canada's national online catalogue, for records of all theses in the National Library of Canada's theses collection, which was established in 1965. You can also access and search for free the full text electronic versions of Canadian theses and dissertations that were published from the beginning of 1998 to August 31, 2002.

Center for Research Libraries foreign dissertations

DART-Europe E-theses Portal (DEEP)
European Working Group of the Networked Digital Library of Theses and Dissertations (NDLTD). Access to 106,000 doctoral theses.

Digital Library and Archives
Digital Library and Archives allows searching for citations and abstracts of over 6,700 theses and dissertations.  Free full-text access is provided for over 4,500 of these items.