To locate books, try GW Libraries Search - Advanced Search, placing the term psychology in the top search box. Add other search terms in the additional search boxes that relate to your topic. Examples might include:
You may wish to use even narrower terms, such as a particular theorist, psychological theory, mental illness, or population group.
Psychology encyclopedias can be found in the reference section on the first floor under these call number ranges; also, books can be found under these ranges on the 4th and 6th floors of Gelman.
BF 1.900: Psychology
RC 321-429: Neurosciences
RC 435-571: Psychiatry