All-Time Roster

List of every X-Men.

List of ad-hoc X-Men rosters.

Images of X-team rosters.
X-Men (60s - 80s)
The X-Men had only one title before 1991 in Uncanny X-Men. Secondary titles started to be published in the 80s.

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Formed by the original X-Men, X-Factor publicly posed as humans who claimed to capture dangerous mutants; in truth they rescued young mutants to protect and train them. X-Factor hired Cameron Hodge to handle public relations, unaware that he was actually generating media hype against mutants. The members of X-Factor rejoined X-Men following a battle with the Shadow King.
X-Factor #1 (1986) - #70 (1991)

Student team of that era.
New Mutants #1 (1986) - #100 (1991)

British-based team made up of several former X-Men.
Excalibur #1 (1987) - #125 (1998)
X-Men (1991 - 2001)
 A second X-Men title was published in 1991. There were now two X-Men titles in this era: Uncanny X-Men and X-Men vol. 2. The former featured the Gold Team while the latter featured the Blue Team. After a few years, both teams merged and X-Men members appeared in both titles. 

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Shortly after taking over as mentor of the student team New Mutants, Cable re-organised it into the paramilitary X-Force a mutant strike team that would take a more proactive stance against threats to mutantkind.
[Replaced New Mutants]
X-Force #1 (1991) - #129 (2001)

X-Factor (Federal Team)
Federal sanctioned team led by Havok.
X-Factor #71 (1991) - #149 (1998)

British-based team made up of several former X-Men.
Excalibur #1 (1987) - #125 (1998)

Student team during of that era.
Generation X #1 (1994) - #75 (2001)
X-Men (2001 - 2008)

The turn of the century saw writer Grant Morrison take over the X-Men title in 2001 to kick-start a revamp of the X-Franchise. All secondary X-titles were cancelled to focus on the X-Men. 

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2000s X-Men: New X-Men

New X-Men
X-Men vol. 2 was re-titled New X-Men with #114 and became the flagship title. The X-Men opened the doors of the Xavier Institute to a large student body and Professor X adopted a more proactive stance.
New X-Men #114 (2001) - #150 (2003)

Uncanny X-Men
Uncanny X-Men took a backseat, featuring a team of X-Men operating outside the Xavier Institute.
Uncanny X-Men #395 (2001) - #443 (2003)

Xtreme X-Men
A new title Xtreme X-Men was published featuring Storm's team search for the prophetic Destiny's Diaries. Storm's team later become the government sanctioned Xtreme Sanctions Executive team.
Xtreme X-Men #1 (2001) - Xtreme X-Men #46 (2004)

New Mutants (vol. 2)
A student title was published featuring students mentored by former members of the New Mutants.
New Mutants #1 (2003) - New Mutants #13 (2004)
(Check New Mutants (vol. 2) section of Institute Student Body)

Grant Morrison's departure from the New X-Men title in 2004 led to a new round of revamp known as ReLoad. 
A new title with the cast largely from the New X-Men title. It became the flagship title featuring Cyclops' home team.
Astonishing X-Men #1 (2004) - #24 (2008)

Uncanny X-Men
The government sanctioned Xtreme Sanctions Executive team led by Storm from Xtreme X-Men moved to Uncanny X-Men
Uncanny X-Men #444 (2004) - Uncanny X-Men #474 (2006)
The title later features a team of X-Men travelling to space to stop the threat of rogue X-Man Vulcan. 
Uncanny X-Men #475 (2006) - Uncanny X-Men #499 (2008)

X-Men (vol. 2)
New X-Men returned to its X-Men (vol. 2) title. The away team from Uncanny X-Men shifted to this title.
X-Men vol. 2 #157 (2004) - #187 (2006)
The title later features a team of X-Men led by Rogue consisting of several ex-villains such as Mystique and Sabretooth.
X-Men vol. 2 #188 (2006) - X-Men vol. 2 #207 (2008)

New X-Men: Academy X
New X-Men: Academy X replaced New Mutants (Vol. 2) as the student book. 
New X-Men: Academy X #1 (2004) - #19 (2006)
(Check the New X-Men: Academy X section of Institute Student Body)

Excalibur vol. 3
Professor X and Magneto work with a team of mutants to rebuild the devastated mutant island of Genosha.
Excalibur vol. 3 #1 (2004) - #14 (2005)

The end of the House of M crossover brought about M-Day, when more than 90% of mutants lost their powers. New X-Men: Academy X was renamed New X-MenExcalibur vol. 3 was replaced with New Excalibur and X-Factor vol. 3 was launched.

New X-Men 
New X-Men: Academy X was renamed New X-Men (Vol. 2) following the House of M event.
New X-Men #20 (2006) - #46 (2008)
(Check the New X-Men section of Institute Student Body)

Investigation agency led by Jamie Madrox.
X-Factor vol. 3 #1 (2005) - #27 (2008)

New Excalibur
New Excalibur #1 (2005) - #24 (2007)
X-Men: Die by the Sword #1 (2007) - #5 (2007)

This era ended with the Messiah CompleX crossover and the X-Men's relocation to San Francisco.
Utopia-era X-Men (2008 - 2011)

Shortly after relocating to San Francisco, the X-Men was attacked by Norma Osborn's Dark Avengers and Dark X-Men. The X-Men relocated to the island Utopia, built from the remains of Magneto's former Asteroid M base, off the coast of San Francisco. 
The flagship X-Men title in this eraThe post also contains a list of active X-Men mutants who stayed on the island Utopia from its establishment to Regenesis
Uncanny X-Men Vol. 1 #500 (2008) - #544 (2011)

Professor X traveled to recover the missing pieces of his life, eventually helping Rogue recover her powers. Rogue returned to the X-Men in Utopia where she became a mentor to the younger mutants.
X-Men Legacy Vol. 1 #208 (2008)  - #260 (2011)
[X-Men Legacy was formerly New X-Men Vol. 1/X-Men Vol. 2]

A small team of X-Men led by Cyclops.  
Astonishing X-Men #25 (2008) - #47 (2012)

Strike team led by Wolverine.
X-Force (vol. 3) #1 (2007) - #28 (2010)

Young X-Men
Student Team mentored by former New Mutants
Young X-Men #1 (2008) - #12 (2009).
(Check Young X-Men section of Institute Student Body)
Title was replaced by New Mutants

X-Men squad comprising of former New Mutants members
New Mutants (vol. 3) #1 (2009) - #32 (2011)

Investigation agency led by Jamie Madrox.
X-Factor vol. 3 #28 (2008) - #229 (2011)
X-Factor vol. 3 changed its numbering after #50 to #200.

New Warriors
Team made up of former mutants who were give technological-based powers.
New Warriors #1 (2008) - #20 (2009)

Following the Second Coming crossover in 2010, X-Force was ended and replaced with Uncanny X-Force. Generation Hope is launched as the student title. A new X-Men title was also launched shortly after.

Uncanny X-Force
Strike force led by Wolverine.
Uncanny X-Force #1 (2010) - #19 (2011)

Search and rescue team featuring the next generation of new mutants led by the messiah child Hope.
Generation Hope #1 (2010) - #12 (2011)

X-Men (vol. 3)
Cyclops' X-Men interact with the rest of the Marvel universe.
X-Men (vol. 3) #1 (2010) - #19 (2011)
Schism/Regenesis (2011-2012)

A difference of ideas between Cyclops and Wolverine caused both to go their separate ways. Cyclops' X-Men continue to operate on their island home of Utopia off the coast of San Francisco. They were concerned with protecting mutant-kind and the world, while present an intimidating front to those who would threaten mutants. Wolverine's X-Men are concerned with setting up a school for young mutants and protecting them.

Team Cyclops

Uncanny X-Men (vol. 2)
Featuring Cyclops' Extinction team.
Uncanny X-Men (vol. 2) #1 (2011) - #20 (2012)

X-Men (vol. 3)
Cyclops' Security Recon Team.
X-Men (vol. 3) #20 (2011) - #41 (2013)

New Mutants (vol. 3)
X-Men clean up team, featuring members formerly in the New Mutants.
New Mutants (vol. 3) #33 (2011) - #50 (2012)

Search and rescue team featuring the next generation of new mutants led by the messiah child Hope.
Generation Hope #13 (2011) - #17 (2012)

Xtreme X-Men (vol. 2)
Team of X-Men from various dimensions tasked with killing 10 evil Charles Xaviers across dimensions
Xtreme X-Men #1 (2012) - #13 (2013)

Team Wolverine

Featuring Wolverine's X-Men and the Jean Grey School.
Wolverine and the X-Men #1 (2011) - #24 (2013)

Featuring Rogue and a supporting cast of X-Men and students.
X-Men Legacy #260.1 (2012) - #275 (2012)

A team of X-Men based in Jean Grey School serving as heroes.
Astonishing X-Men #48 (2012) - #68 (2013)

Strike force led by Wolverine. Protectors of the Jean Grey School.
Uncanny X-Force #19.1/20 (2012) - #35 (2012)

Investigation agency led by Jamie Madrox. The agency was led by Havok when Madrox went missing.
X-Factor vol. 3 #230 (2012) - #262 (2013) 
Marvel Now (2012 - 2014)

Featuring Wolverine's team.
Wolverine and the X-Men #25 (2013) - #42 (2014)

X-Men Legacy (vol. 2)
Solo title featuring Legion, son of Professor Xavier, on his path to bring change to the world.
X-Men Legacy Vol. 2 #1 (2012) - #25 (renumbered #300) (2014)

Uncanny X-Force (vol. 2)
Proactive team led by Storm.
Uncanny X-Force Vol. 2 #1 (2013) - #17 (2014)

Proactive team led by Cable.
Cable and the X-Force #1 (2012) - #19 (2014)
All-New Marvel Now (2012 - Present)

A list of current teams in their respective titles.