Where you look for a dissertation or thesis depends on the originating institution. There are different resources to search depending on whether you are looking for an MTU dissertation, or a dissertation from a different institution.
You can find dissertations and theses by Michigan Tech students through the library catalog, or through an external database. Both are linked below.
The following links are a few places where you can find dissertations from other institutions. Some library databases also index dissertations in addition to other types of material, so you can check there as well. If you find one of interest, use InterLibrary Loan to request it.