These books are: The Talented Mr. Ripley (1955), Ripley Under Ground (1970), Ripley's Game (1974), The Boy Who Followed Ripley (1980) and Ripley Under Water (1991). It is alleged that Ms. Highsmith coined the self-effacing and jocular term "Ripliad" herself, although when an anthology of the first three of these novels was published by Everyman's Library in 1998, critics used the term "Ripliad" to refer to those specific three. (In 2011 the Folio Society of London brought out its own three-volume boxed set of exactly the same novels.) However, the first boxed set of all five Ripley novels did not appear until 2008 (THE COMPLETE RIPLEY NOVELS); to them, the term "Ripliad" also applies.
(from blog librarything.com)