Uncanny X-Men #266 features what is labeled as the 1st full appearance of Gambit.  However we know that Gambit actually appeared EARLIER in Uncanny X-Men Annual #14.  The debate rages as to which of these appearances is the first FULL appearance!  Better get both for your collection to be sure.  This book has a cool Andy Kubert Gambit cover appearance, so it seems to be the preferred choice amongst collectors for the time being.  This book is graded 9.6 NM+ with white pages by CGC.  It's alignment is perfect.