Nature-based solutions (NBS) are increasingly being adopted to address climate change, health, and urban sustainability, yet ensuring they are effective and inclusive remains a challenge. Addressing these challenges through chapters by leading experts in both global south and north contexts, this forward-looking book advances the science of NBS in cities and discusses the frontiers for next-generation urban NBS. NBS are fundamentally inter- and transdisciplinary approaches that require systems thinking and multi-level governance. With a focus on the multiple challenges that cities face, from heat and air pollution to storm water and threats to human health, this book puts forward a diversity of ideas for embracing complexity in mainstreaming NBS and inspiring new approaches to create the ecological urban futures we need. Speaking to the need for cities around the world to employ ecological, nature-based design, this book will be essential reading for early career professionals, practitioners, scholars, and students across multiple disciplines engaging with nature-based solutions including urban ecology, design, architecture, landscape architecture, geography, urban planning, policy, and management.