"The Concentration City" is a dystopian short story by British author J. G. Ballard, first published (as "Build-Up") in the January 1957 issue of New Worlds.
Ballard retitled the story for its inclusion in the 1967 collection The Disaster Area;[1] it has been republished in Billennium and Chronopolis, and appears in volume one of The Complete Short Stories of J. G. Ballard.[2]