WildC.A.T.s/X-Men was a crossover event by Image Comics (from Jim Lee's WildStorm) and Marvel Comics in 1997 and 1998 that featured WildStorm's WildC.A.T.s meeting Marvel's X-Men. Originally released in four individual comics, each representing a different "age," the series was later collected by Image Comics/WildStorm as a trade paperback (ISBN 1-58240-022-9) in December 1998. Source: Wikipedia (en)