When U.S. Copyright Law was revised in 1976, registration and notification requirements were eliminated. Your work is automatically copyrighted as soon as you fix it in some medium (paper, computer disk, videotape, etc.).
You are not required to place a copyright statement on your work or register it with the copyright office, but it is a good idea to consider doing one or both. A copyright notice advises potential users that the work is protected and identifies you as the copyright holder. Registration is required before you can bring a lawsuit against someone who has infringed on your copyrights.