This book constitutes the proceedings of this year's Sustainable Smart Cities and Territories International Conference (SSCt 2021), held in Doha, Qatar, from the 27th to the 29th of April 2021. The SSCt 2021 is an open symposium that brings together researchers and developers from academia and industry to present and discuss the latest scientific and technical advances in the fields of Smart Cities and Smart Territories. It promotes an environment for discussion on how techniques, methods, and tools help system designers accomplish the transition from the current cities towards those we need in a changing world. The program includes keynote abstracts, a main technical track, two workshops, and a doctoral consortium. The symposium is organized by the Texas A&M University at Qatar. We would like to thank all the contributing authors, the members of the Local Committee, Scientific Committee, Organizing Committee, and the sponsors (Texas A&M University of Qatar, AIR Institute and the IoT Digital Innovation Hub) for their hard work and dedication.