On March 4, 2019, the United States Supreme Court issued its unanimous decision (available here) in Fourth Estate v. Wall-Street.com. The Court held that 17 U.S.C. § 411(a), which states that “no civil action for infringement of the copyright in any United States work shall be instituted until . . . registration of the copyright claim has been made in accordance with this title,” means that the Copyright Office must register the copyright before a lawsuit is filed. The Court rejected the argument that simply filing an application to register the copyright was sufficient to file a lawsuit.
The Copyright Office often takes many months to register a copyright (the average time presently is seven months, although expedited processing of registration is available for an additional $800 fee), so copyright owners are well advised to submit their copyright applications in a prompt manner. (There are limited statutory exceptions to the registration requirement, such as for those works vulnerable to predistribution infringement (e.g., a movie or musical composition).)
Note that, upon registration, a copyright holder can recover for infringement that occurred both before and after registration.