Theses (sing. "thesis") - refers to a longer academic paper typically required to earn a Master's degree.
Dissertation - an even longer work than the thesis (100+ pages), and required for most doctoral degrees. Often dissertations are later published as academic books (also referred to as monographs).
Recognizing a thesis or dissertation in your search results
In the library catalog: “ Thesis/dissertation”
In library databases (e.g. PsycINFO) OR
Sample library catalog searches:
thesis m.a. wheaton college (for Master’s theses)
thesis ph.d. wheaton college (dissertations, Bible and theology)
thesis psy.d. wheaton college (dissertations, clinical psychology)
“action research paper” wheaton college (for MAT theses)
In most cases, you will cite only published secondary sources in an academic paper, and theses and dissertations are not considered published works. However, they can be very useful and it’s legitimate to even reference them in a bibliography, especially when there’s little else on your topic. Consult with a subject librarian if that’s the case.
More commonly, it is the bibliographies in theses and dissertations that are most valuable to a researcher. Doctoral students in particular are expected to conduct a comprehensive and up-to-date search of the literature related to their topic. Take advantage of their time and effort and save yourself the same.