Every X-Men movie in order
The X-Men timeline is famously tangled. The prequels start in the 1960s, Days of Future Past rewrites history, and Wolverine and Deadpool go their own way. This order follows the story as it happens, from X-Men Origins: Wolverine to Deadpool & Wolverine.
With the X-Men joining the Avengers in Avengers: Doomsday, it's a good time to catch up. The essentials cover the films that matter most.
The X-Men watch order

X-Men Origins: Wolverine

X-Men: First Class

X-Men: Days of Future Past

X-Men: Apocalypse

Dark Phoenix

X-Men

X2

X-Men: The Last Stand

The Wolverine

Deadpool

Deadpool 2

The New Mutants

Logan

Deadpool & Wolverine
Questions
What order should I watch X-Men in?
Start with X-Men Origins: Wolverine and follow the list above, which has all 14 X-Men titles in story order. For the shortest route, stick to the 6 essentials.
How long does it take to watch all of X-Men?
About 28 hours for the 14 titles out so far. The 6 essentials take about 13 hours.
Where do I start with the X-Men movies?
For the story in order, start with X-Men Origins: Wolverine and X-Men: First Class. For the classic experience, start with X-Men (2000) and X2, then watch the prequels.
Are the Deadpool movies part of the X-Men timeline?
Yes. Deadpool and Deadpool 2 are set in the X-Men universe, and Deadpool & Wolverine carries it into the Marvel Cinematic Universe.
Watch X-Men in order with Chronologica
Mark titles as you watch, stick to the essentials and always know what's next. No account needed.