Find Theories and Theorists
Depending on the theory and theorist, this information can be difficult to find. Keep in mind that some theories were developed some time ago even if they are still in use today. This may mean that information is limited or that you will need to request items through Interlibrary Loan (ILL).
Articles and Ebooks
The best place to start to find theory and theorist information is the library catalog through the library homepage. Use precise language such as theory titles and theorist names to see resources that are related to those topics and people. You will find a variety of resources including: academic articles, newspaper articles, videos, transcripts, and ebook chapters.
For primary resources written by the theorists:

Videos
The video databases linked below contain videos of theorists and theory information. Search by theorist name or theory name. For example, here is a search in Psychotherapy.net:
