X-Men (1963)

The X-Men was the title that first introduced mutants into the Marvel Universe (though Namor would later be categorized as a mutant and his creation pre-dates the X-Men). The initial run of the X-Men was not as popular as other titles of the era and was eventually cancelled, continuing only as a reprint series before being relaunched with a new team and new creators. The book took off with issue #94, the first issue featuring this new direction, and continued to grow in popularity, dominating sales charts for years to come. The book was finally cancelled in 2011 only to be relaunched the next month with a new number one issue the next month.

Original Run (1963-
1, 2, 3

Stan Lee, Jack Kirby, Roy Thomas, and Neal Adams

Reprint Era
Reprints

The All-New All-Different X-Men
Claremont and Cockrum

Claremont and Byrne Era
Dark Phoenix Saga

Cockrum Returns
Brood Saga

Paul Smith Era
Morlocks, Storm, and Madelyne

John Romita Jr Era
Mutant Massacre

Marc Silvestri Era
Fall of the Mutants Inferno

Jim Lee Era
X-Tinction Agenda

Gold Team Era
Byrne Returns Fatal Attractions

Phalanx Covenant

Onslaught

Steve Seagle Run
Hunt for Xavier

Alan Davis Era
Magneto War The Twelve

Revolutions
The Neo

New X-Men
Joe Casey and Chuck Austen

New Age
Claremont and Davis Return End of Greys

Brubaker Era
Rise and Fall of the Shi'ar Empire

Fraction Era
Utopia, Nation X, Second Coming

Schism
Kieron Gillen

Significant Issues
#1 - First Appearances of Professor X, Cyclops, Jean Grey, Beast, Iceman, Angel, and Magneto

#2 - First Appearances of Fred Duncan and the Vanisher.

#3 - First Appearance of the Blob.