This book provides multidisciplinary approaches to smart and sustainable urban ecosystems. Urbanization is a global tendency, and up to 70% of the world population is projected to live in cities by 2050. How will this rapid urbanization alter the face of the world? What are the environmental consequences of megacities' expansion? What are smart solutions to make life in cities safe, comfortable, and environmentally friendly? These and other important questions are addressed by the conference Smart and Sustainable Cities (SSC). This year's theme for the conference will be « Sustainable urban ecosystems: challenges and solutions». Megapolises are complex ecosystems. Air and water quality, vegetation, and soils in megapolises are exposed to anthropogenic influence. Studying negative environmental consequences of the anthropogenic and technogenic pressures is among the key tasks of urban ecology and environmental impact assessment. Advanced approaches and smart technologies to monitor, model, and assess environmental consequences and risks in megapolises will be widely discussed at the conference. Searching for solutions of the environmental problems of modern megapolises will be the key point of the conference. Successful experiences of sustainable urban development and nature-based solutions to support climate adaptation, carbon neutrality, and human health will be presented in the conference proceedings.