These phonebook-sized, B&W, value-priced collections each contain about 25 issues of consecutive X-Men continuity, starting with X-Men #1.
Together, these 3 volumes contain the entire run of X-Men (plus Beast's solo adventures in "Amazing Adventures") before the book became a series of reprints and later became relaunched with "Giant-Size X-Men #1" and "Uncanny X-Men #94".
The volume was originally called Essential Uncanny X-Men, but with issue two Marvel changed the name to Essential Classic X-Men. Since then, reprints of the first volume have been renamed Essential Classic X-Men as well.
— Description from Comic Vine community (comicvine.gamespot.com · https://comicvine.gamespot.com/essential-classic-x-men/4050-23936/).
