Obtain a copyright registration form from the U.S. Copyright Office or register to complete a form online through the Copyright Office's Website. Online registration has some benefits including a lower filing fee and the ability to upload your screenplay to the Copyright Office rather than mailing a copy.
Complete the registration application form. Under the section of the application that asks what type of work you are registering, select "Literary Work." If the screenplay has multiple authors, you may enter multiple parties in this section of the application and the copyright will be registered as a joint work. Remember that all resulting profits must be split equally with co-authors unless you have an agreement to the contrary.
Upload your screenplay to the Copyright Office's Website through the procedures outlined in their application. Mail your screenplay to the Copyright Office if you decided to use a paper application.
Submit your completed copyright application and the applicable filing fee to the Copyright Office.