REGISTER WITH THE WRITER’S GUILD OF AMERICA (www.wga.org) Screenwriting Protection
Aside from copyrighting your screenplay with the Library of Congress, it’s a good idea to register your script with the WGA, a guild designed solely for the purpose of helping screenwriters and protecting screenplay intellectual property rights. You can utilize the script registration process on their website even if you are not a professional screenwriter's guild member.
If you are a screenwriter and live east of the Mississippi register your story, outline, treatment, screenplay/material with the WGA East. If you are a screenwriter and live west of the Mississippi register your material with the WGA West. If you live on the Mississippi river… I don’t know what to tell you. But I’m sure you’ve got a great story to tell, and Hollywood will love to read it one day... if your scriptwriting format and conventions of the screenplay are industry standard. (for formatting advise buy The Bare Bones Book of Screenwriting at Amazon and screenwriting software.)
You can mail in a hardcopy of your final draft screenplay or do the process online at the www.wga.org website. The cost is $20 for non-guild members and $10 for screenwriter guild members in good standing. Script registration is valid for a term of five years.