This book constitutes the thoroughly refereed proceedings of the 4th Ibero-American Congress, ICSC-CITIES 2021, held in Cancún, Mexico, in November - December 2021. Due to the COVID-19 pandemic the conference was partially held online. The 21 full papers and one short paper presented were carefully reviewed and selected from 112 submissions. The papers are organized in topical sections on ​computational intelligence for smart cities; urban informatics; internet of things, smart energy and smart grid.