Copyright law protects written work like sitcom scripts even if they have not been registered with the U.S. Copyright Office. But if someone steals your work, you can't take them to court until you have registered. Copyright registration will also help prove that you wrote the script, and it will allow you to collect additional remedies such as attorney fees if you win. So registering your script is probably a good idea if you are concerned about protecting your rights.
Begin a registration. From the U.S. Copyright Office website, go to "Electronic Copyright Office" and follow the instructions to register and log in. Then start a new copyright registration. When asked what type of work you want to register, choose "Work of the Performing Arts."
Enter the title of your script. If you have a collection of unpublished scripts -- if you've written several episodes, for example -- you can generally register them all at once unless they have different authors or copyright owners. To do this, make up a title for the whole collection and add it as the "Title of the Work Being Registered." Then, add the titles of each individual script as "Contents Titles."
Enter your script's publication status -- probably "unpublished," unless you've distributed it to the public somehow. Showing it to potential buyers or to other writers for advice generally doesn't count as publication.
Enter the script's author. If more than one person worked on the script, make sure to list them all and describe each author's contribution ("editing," for example). If writing the script was part of an employee's job, then it was "made for hire" and the employer is considered the author. This doesn't apply to freelancers unless they have a contract that specifically says it does.
Enter the copyright claimant, which is the person who owns the rights to the script. This is the same as the author, unless you have sold your rights to the script to someone else.
Enter information on other works. Sitcom scripts are often partly based on elements of the show, like characters or key phrases, which are already copyrighted. If your script contains such elements, then make note of it under "Limitation of Claim."
Enter copyright management contact information. This is the person people should contact if they want permission to use your script. This will generally be you, but if you belong to a writer's guild or other organization that represents its members in copyright negotiations, you can enter its contact information instead.
Fill out the rest of the form. The website will ask for various contact information and for your promise that you have the right to register the script.
Pay the filing fee. The website will prompt you to pay by credit or debit card or by electronic funds transfer. You can find the current fees on the Copyright Office website.
Submit copies of your script. If your script is unpublished, you need to send only one copy; otherwise, you need to send two. If the script has not been published, or if it has only been published electronically, you can upload an electronic copy through the website. Otherwise, you will have to enter information about mailing copies. If you have to mail your copies, make sure to do it within 30 days. Submitting the necessary copies completes your application. The Copyright Office will take several months to process the application and then will send you a certificate of registration.