There is a growing movement to make cities “smarter.” Typically the goal is to enhance a city’s efficiency and sustainability and thus lower carbon footprints. While these efforts are well-intended and of great importance, we must also make sure that our future cities are places that people also desire to live in across their lifespan. Against this backdrop, a European Union-funded COST (European Cooperation in Science and Technology) Action was undertaken from 2013-2017 entitled People-Friendly Cities in a Data Rich World. The Action culminated in a two-day Participatory Urbanism 2017 conference that brought together researchers, scientists, city planners, architects, public officials, urban activists, businesses, and NGOs from 30 countries. A crucial goal of this conference was to solicit both guiding principles and research questions that should be pursued in the quest to make cities more liveable for people and smarter for the planet. Here we present the main findings. Ultimately, it is hoped that these findings will help guide the creation of people-friendly cities in a data-rich world.