Krupski (P), tripped over a cable and fractured her femur while she was on board the cruise ship Costa Magica. The ticket required an injured party to submit 'written notice of the claim with full particulars . . . to the carrier or its duly authorized agent within 185 days after the date of injury.' The ticket further required any lawsuit to be 'filed within one year after the date of injury' and to be 'served upon the carrier within 120 days after filing.' P's counsel notified Costa Cruise Lines of Krupski's claims. The parties were unable to reach a settlement, and three weeks before the 1-year limitations period expired, P filed a negligence action against Costa Cruise, invoking the diversity jurisdiction of the Federal District Court for the Southern District of Florida. Krupski served Costa Cruise on February 4, 2008. Over the next several months, after the limitations period had expired, Costa Cruise brought Costa Crociere's (D) existence to P's attention three times. On June 13, 2008, P responded to Costa Cruise's motion for summary judgment, arguing for limited discovery to determine whether Costa Cruise should be dismissed. With her response, P simultaneously moved to amend her complaint to add D. The court denied Costa Cruise's motion for summary judgment without prejudice and granted Pi leave to amend. P filed an amended complaint on July 11, 2008, and served D on August 21, 2008. The District Court issued an order dismissing Costa Cruise from the case pursuant to the parties' joint stipulation, Pi apparently having concluded that Costa Cruise was correct that it bore no responsibility for her injuries. D moved to dismiss, contending that the amended complaint did not relate back under Rule 15(c) and was therefore untimely. Because Costa Cruise informed P that D was the proper defendant in its answer, corporate disclosure statement, and motion for summary judgment, and yet P delayed for months in moving to amend and then in filing an amended complaint, the court concluded that P knew of the proper defendant and made no mistake. The Eleventh Circuit affirmed in an unpublished per curiam opinion. The Supreme Court granted certiorari to resolve tension among the Circuits over the breadth of Rule 15(c)(1)(C)(ii).