Some writers don't like to use their real names with their work. A pseudonym, or pen name, allows you to express yourself without revealing your true identity, and costs as little as $10 to register.
Search the U.S. Copyright Office's database and local directories to make sure no one is using the pen name you want to use, particularly if they publish the same type of work as you. Contact the county clerk and secretary of state to make sure no one has registered the name as a trade name, also known as a DBA ("doing business as") or assumed name.
File a DBA form with the county clerk. A DBA costs between $10 and $100 as of 2011, and though it will allow you to represent yourself with your pen name in business, you will still have to sign legal documents with your real name. Check with city hall and the secretary of state to find out whether you must file a DBA with these offices.
Register your works with the U.S. Copyright Office under your pen name. You might include your real name on the copyright claim if you want to make it apparent that you use a pen name, or you might choose to remain anonymous. Copyright exists as soon as you produce a work, but to be able to legally claim someone has infringed upon your copyright, you must officially register it. The fee to register a copyright claim starts at $35.