There are many ways to find past theses. Some are free and some are subscription resources.
City University Library holds print copies of PhD and for example DPsych theses submitted by our research students. Theses can be searched via the library catalogue by subject/ keyword and then click Thesis on the left hand side to refine your search.
Electronic theses, especially the more recent ones are often held in institutional repositories such as City Research Online
EThos Electronic Theses Online Service
EthOS is a British Library Service which aims to offer a single point of access for PhD theses submitted at UK Higher Education Institutions. The database contains over 250,000 records of doctoral dissertations. Some theses are available for immediate download and more are digitised each year. You need to sign up for an account to use EThos.
The Index to theses database contains references of over 580,000 theses submitted at Universities in Great Britain and Ireland from 1716 to present. An abstract is usually included for theses submitted after 1986.
ProQuest Dissertations & Theses (PQDT)
ProQuest Dissertations & Theses (PQDT) database is a comprehensive collection of dissertations and theses from around the world offering full text for graduate works added since 1997 with selected full text for works written prior to 1997.
As more and more doctoral dissertations are digitised it is often possible to access the abstract or the full-text dissertation online. Here is a list of resources you could use to search for theses on the topic of your research.
ADT – Australasian Digital Theses Program, provides access to digital versions of theses produced by postgraduate research students at Australian Universities.
Cybertesis This Portal, developed by the University of Chile provides easy access to full text electronic thesis published in different universities of the world.
DART-Europe E Theses Portal allows you to search and access full-text dissertations from 324 Universities in 19 European countries including the UK. You can view list of participating institutions. You can use the Advance search option to limit your results to one or more languages.
dissertations.se to search and download dissertations from Swedish Universities written in English. Half of the documents on this website are available for immediate download as a PDF.
DiVA is a portal for research publication and students dissertations from 28 Universities in Sweden and Norway.
DSpace@MIT contains more than 25,000 master and doctoral dissertations completed at MIT dating as far back as the mid 1800’s. Full-text is available for dissertations submitted after 2004.
Kiwi Research Information Service is a gateway to the open-access research documents produced at universities, polytechnics, and other research institutions throughout New Zealand.
NARCIS The National Academic Research and Collaborations Information System was developed to increase the visibility and retrieval of Dutch scientific research. NARCIS facilitates access to open access publications from the repositories of all the Dutch universities, Koninklijke Nederlandse Akademie van Wetenschappen (KNAW), Netherlands Organisation for Scientific Research (NWO) and other research institutes.
The Networked Digital Libraries of Theses and Dissertations catalogue contains more than one million records of theses and dissertations.
OAIster is a union catalogue including more than 25 million records representing digital resources from 1,100 contributors.
OpenDOAR is a directory of academic open access repositories. Search repositories together or individually.
(With thanks to my colleague Antonella for providing the links and information).