This book constitutes the thoroughly refereed proceedings of the Third Ibero-American Congress, ICSC-CITIES 2020, held in Costa Rica, in November 2020. Due to the COVID-19 pandemic the conference was held online. The 21 full papers presented were carefully reviewed and selected from 99 submissions. The papers are organized on topical sections on Energy Efficiency and Sustainability; Mobility and IoT; Infrastructure, Environment, Governance. .