This is the first book-length study to examine the enduring popularity of block-buster films based on DC or Marvel superhero comics properties. It argues that the success of superhero movies is rooted in aesthetic practices unavailable to other types of film, and suggests that the multi-dimensional seriality of these movies, combining practices of serialisation, adaptation, and transmedia storytelling, endows them with an unmatched potential to engage audiences over time and to actively intervene in the discourses of online fandom. The book develops a critical theory of digital-era popular seriality, examining the narrative strategies of superhero movies and their evolution, from 1978's Superman to 2018's Avengers: Infinity War and beyond. It discusses textual and extra-textual practices of fan mobilisation, and considers the genre's shared political imaginary and its purchase on contemporary political debates.