Eighty-five per cent of humanity-some nine billion people-will live in cities by the end of this century (OECD Publishing, 2015). While uncertainty surrounds any attempt to look this far into the future, an unquestionable consequence of this oft quoted statistic is that securing the sustainability of our planet is increasingly an urban challenge. Environmental protection, green economic growth, social equality, clean energy, decarbonization, mobility, and health are all best addressed in cities (Short, 2017;Bai et al., 2018). If cities can become sustainable, then we will have gone a long way to fixing many of the problems that we and our fellow species face. The question of course is how to do this. While we now know what the core problems and many of their solutions are, change is not happening at anywhere near the scale and pace required. Cities need to rapidly curb greenhouse gas emissions, reinvent their economies, and address growing inequalities, all in the face of obdurate infrastructures and buildings, huge demographic shifts, rapidly evolving technologies and hostile funding conditions.As the practice of organizing collective action to steer society toward specific shared goals (Kooiman, 1993), governance is critical in enabling cities to address these challenges. Governments, communities, NGOs, private companies, utilities, universities, unions, and others are realizing the need to work collectively to respond to the pace, scale and scope of urban change. UN Habitat recognizes that working with cities is the best way to address global challenges (Parnell, 2016;Acuto, 2018), while the OECD Publishing (2015) highlights that good governance is particularly crucial in cities due to their density of connections and role as key drivers of development. The focus of governance on who is involved in making decisions and what kinds of knowledge gets to count fundamentally frames what is and is not possible in cities, and by extension enables us to understand how they might be reconfigured to make more sustainable actions possible. Governance underpins the UN Sustainable Development Goals through the enabling goal 17 on strengthening partnerships, while cities have emerged as leaders in the field of climate action through networks such as the C40 Cities Climate Leadership Group, which connects 90 of the world's most influential cities, representing more than 650 million people and one quarter of the global economy. The importance of cities to the sustainability agenda is further heightened by the resurgence of populist national governments around the world that are apathetic or openly hostile to the environmental agenda. The future sustainability of humankind, in both the mundane sense of how day-to-day existence will be for the majority of us to the viability of the planet itself, will be shaped in and by cities. Understanding cities and how they can be governed in more innovative, inclusive and effective ways is now a global sustainability priority in ways that it has not been before.The Governance and Cities s...