If the work infringed upon is of U.S. origin, then you must register your copyright before filing a lawsuit. ^[1] If the infringement took place before you registered your copyright, then you can sue for your actual damages, but you generally will not be able to recover attorney’s fees or statutory damages. However, there is a three-month grace period for published works, so if you register your copyright within three months of publication, you can recover statutory damages and attorney’s fees for any infringement that takes place after publication. ^[2]

1. 17 U.S.C. §411.
2. 17 U.S.C. §412.