In the United States, both theses and dissertations:
A thesis is sometimes required for a master's degree, but not all master's programs require one. (I have two master's degrees and neither required a thesis.)
A dissertation is almost always required for a doctoral degree. Since most doctoral degrees take several years, the research project for a doctoral degree may have a bigger scope than research done for a master's degree. Not surprisingly, then, a dissertation is likely to be much longer than a thesis.
In the past, theses and dissertations were only been available at the college or university that granted the author's degree. (It's very different from books - most books can be found at several different libraries around the world.) Lucky for us, this model is changing!
Nowadays, more and more schools are requiring their students to submit their theses or dissertations to something called an institutional repository. Institutional repositories are online, and everything in them is freely available to anyone. That said, you don't have time to go to each and every college's institutional repository - and there are better ways you can search for theses and dissertations.
There are two main ways you can find freely available theses and dissertations:
Most institutional repositories are hosted by individual colleges and universities. It would take way too much time for you to search every single school's repository, so I would recommend searching some of these "aggregator" sites below. They'll search any institutional repository they can find - so you'll be able to more easily find all the dissertations or theses on your topic.
Although the library provides database access to ERIC, you can also search ERIC directly from their website. It's a bit easier to find theses and dissertations from the website instead of the library database:
Go to the ERIC website.
Enter your search terms and check the box that says Full text available on ERIC.
Scroll down the results page until you see a box on the left that says Publication Type. You will likely have to click More to see Dissertations/Theses as an option.
That's it! All your search results should be available as PDFs.
Let's look at a few example citations, and then review their format.
Jackson, P.P. (2016). Teachers' perceptions of English language learners and reading instruction (Doctoral dissertation, Walden University). Walden Dissertations and Doctoral Studies. https://scholarworks.waldenu.edu/dissertations/
Lezama, S.M. (2014). Equal education: School leaders support of English language learners' academic success (Doctoral dissertation, California State University, Fullerton). PQDT Open.
Mandell, E. (2018). Three art teaching strategies to support language acquisition and communication skill development in English language learners (Master's thesis, Moore College of Art & Design). ERIC.
Riddle, S.A. (2017). Orthographic skills in English language learners and stuents with learning disabilities (Doctoral dissertation, Temple University). Temple University Electronic Theses and Dissertations. https://digital.library.temple.edu/digital/collection/p245801coll10/
You can see all the citations have the following elements in common:
They begin with author's last name, followed by first initial and middle initial (if they use one).
The year of publication, in parentheses, followed by a period.
The dissertation or thesis title, in italics. As with articles, everything should be lowercase except:
NOTE: Do not put a period right after the title - the period comes later.
In parentheses, and not in italics, either the phrase "Master's thesis" or "Doctoral dissertation", followed by a comma, and then the name of the school that granted the degree. After the parentheses, add a period.
What comes next depends on where you found the thesis or dissertation.
If you found it using OATD or NDLTD, you would follow the link in the description. For example, this is a search result from NDLTD, and you can see it includes a link to Walden University's website at the bottom.
In this case, you'd link to Walden University's website. You'll also use the name of their site in your citation - see examples #1 and #4 above.
If you found the thesis or dissertation using ERIC or PQDT Open, you will put the site name, since you can access the PDFs directly from those sites.
See examples #2 & #3 above.