Costa Diadema is a Dream-class cruise ship owned by Carnival Corporation and operated by Costa Crociere. The ship was ordered in October 2012 and was delivered to Costa on 25 October 2014. At her time of delivery, Costa Diadema was the largest vessel to fly an Italian flag and was Costa's largest vessel at the time; she is formerly Costa Crociere's flagship being replaced by the Costa Toscana.

The Dream class is a class of cruise ships, operated by Carnival Cruise Lines and Costa Cruises, The lead vessel of the class, Carnival Dream, entered service in September 2009.