In a new ratcheting up of the endless interactions possible with a cinematic universe, the Guardians of the Galaxy will appear in Avengers:  Infinity War.  Vin Diesel revealed the appearance in a Facebook video, according to Variety.

This will bring together two sides of the Marvel Cinematic Universe, the earth-based superheroes and the science fiction stories, in one film.  At some point, expect the supernatural area of the Marvel universe (see "Marvel Opening Third Side of Movie Universe") to also cross over with the other two.

The Guardians of the Galaxy characters will next appear in their own feature, Guardians of the Galaxy Vol. 2, in May 2017 (see "Best in Shows – Q2 2017").

Avengers: Infinity War will premiere one year later, in May 2018 (see "Best in Shows – Q2 2018").