Inspired by this weekend's release of X-Men: Days of Future Past, I wanted to examine the comic book source material for each of the movies in the X-Men franchise to date.
In the bottom row, I arrange the X-Men movies in order of continuity. Nearly all of them have sequences that occur long before or after the central events of the film, but I've sequenced them relative to those central events. For instance, X-Men opens with Magneto's origin during World War II, but most of the film transpires in 2000.
The movies borrow from the comics, but only in a patchwork way, stitching together characters and concepts from different decades. In the top row, I identify the issue featuring a central premise/story-arc of the corresponding movie. Some are obvious: "Dark Phoenix", "Days of Future Past", Logan & Mariko (actually called "Scarlet in Glory"). It's a stretch to say that X-Men is about Wolverine joining the team, but since he is one of only two characters (along with Professor X) to appear in all seven films, the franchise would seem to agree with this connection.
(X-Men Origins: Wolverine draws its inspiration from story arcs written outside the Uncanny X-Men title. I haven't connected the movie to a specific issue, but in terms of comic continuity, Wolverine probably gained his adamantium skeleton between 1945 and 1974.)
The franchise source material clusters between 1975 and 1983, issues all written by X-Men legend Chris Claremont. The movie franchise seems to ignore issues published after 1983, 68% of Uncanny X-Men's story (an even higher percentage if considering the various titles that begun to spin off in 1983, comprising more than a thousand issues). The next film in the franchise, X-Men: Apocalypse (2016), will push this cluster to at least 1986 (first appearance of Apocalypse in the spin-off series X-Factor), but perhaps as late as 2000 ("Age of Apocalypse" story-arc).