Copyright protection is automatic — your work is copyrighted the moment it is created and fixed in a tangible form (written down, recorded, saved to a file). You do not need to register or use the © symbol for protection to exist.
However, registration provides significant benefits:
Ability to sue: You must register your copyright before you can file a lawsuit for infringement in federal court.
Statutory damages: If you register before infringement occurs (or within 3 months of publication), you can seek statutory damages of $750-$30,000 per infringed work ($150,000 for willful infringement) instead of having to prove actual damages.
Attorney fees: Registration before infringement also allows you to recover attorney fees from the infringer.
Public record: Registration creates a public record of your claim, which can deter infringement and simplify enforcement.
Customs protection: Registration allows you to record your copyright with U.S. Customs to help prevent importation of infringing copies.
How to register: File online through the U.S. Copyright Office's electronic registration system. Fees range from $35-$65 for standard applications. Processing typically takes 3-7 months.
For any work of significant value, registration is strongly recommended and is a relatively small investment for the legal protections it provides.