Míriam is right, I believe. I don’t have the particulars, either, but there was a film deal struck with no actual ownership changing hands. There was also another deal done earlier that traded some or all of Marvel’s (Disney’s) existing profit-sharing of the movies for the rights to the merchandise, which seems to have worked out well for Disney (considering the lackluster performance of the last Spider-Man movie).

By the way, I forgot about the Fantastic Four, to which Fox owns the film rights (along with the X-Men). Marvel had apparently been stripped of anything of proven value, but with the benefit of hindsight this did not stop them and parent corporation Disney from creating new and even more successful movie franchises, and now Sony wants Spider-Man to be a part of the MCU gravy train (while retaining its film rights).

If I recall correctly, Sony and Disney cut a deal for Spider-Man to join the upcoming Marvel films (I’m guessing Captain America Civil War and potentially the 3rd Avengers). But Sony didn’t give back the rights, they kind of “borrowed” them. Anyway, that’s how I understood it, I might be wrong. This whole Sony Spider-man thing is very confusing!

But I thought that recently Disney acquired the theatrical rights to Spider-Man, hence the pushback of the last two Avengers movies (and almost every Disney-distributed MCU films for the next four-and-a-half to five years) to rewire the story to fit Spidey in. I guess this must have been in the works before that announcement.

They don’t own the film rights–Sony does. You can own a character without owning every aspect of them, and film rights is a big one. Marvel sold Spider-Man’s film rights to Sony years ago, before Disney purchased Marvel, and likewise X-Men to Fox.

This, by the way, was a big reason why Disney’s purchase of Marvel was widely criticized at first. Beyond the question of fit, people wondered whether Marvel had enough value left in their catalog to justify the price Disney paid. Beyond Spider-Man and the X-Men, which had already been sold, there weren’t really any big-time superheros that were very popular with the general public (people knew about Captain America and the Hulk, but they weren’t big sellers, and Iron Man wasn’t well known outside of the hardcore fandom before that one movie). I guess the question has been answered by now, but at the time it wasn’t a sure thing.