A common question is whether or not a student should file for copyright, which is an option during the ProQuest submission.
Under US copyright law, your work is already, automatically, under copyright. For most students, then, filing for copyright is probably not necessary.
However, filing for copyright does grant certain additional protections that you may want if you want to be able to establish your right to the dissertation in a court of law. According to the U.S Copyright Office:
"In addition to establishing a public record of a copyright claim, registration offers several other statutory advantages:
• Before an infringement suit may be filed in court, registration (or refusal) is necessary for works of U.S. origin.
• Registration establishes prima facie evidence of the validity of the copyright and facts stated in the certificate when registration is made before or within five years of publication.
• When registration is made prior to infringement or within three months after publication of a work, a copyright owner is eligible for statutory damages, attorneys’ fees, and costs.
• Registration permits a copyright owner to establish a record with the U.S. Customs and Border Protection (CBP)3 for protection against the importation of infringing copies."
Even if you choose not to file for copyright during your submission (you can do it through ProQuest), you can choose to file later on, as long as you make the request within the original term of copyright. In the US, copyright lasts until 70 years after the death of the author, so you have some time.
The Scholarly Communications Librarian can consult with you if you have any questions.