While wildlands are increasingly being transformed into managed ecosystems in rural areas around the world, cities are now also being recognized for their “wilderness” areas. Cities and wilderness have a complex relationship based on constantly changing human-nature interactions and social values. Therefore, understanding the complex nature of the urban-wilderness relationship requires approaches from both the social and natural sciences. This special feature seeks to advance our understanding of this relationship by highlighting the many benefits of wild urban ecosystems for people and biodiversity. From a practical perspective, the special feature examines ways of incorporating urban wilderness into contemporary global urban trends such as green space design, green infrastructure, urban biodiversity conservation and sustainable cities. We conclude that engaging with the wild side of cities is a timely issue, offering unique and rarely exploited opportunities for developing liveable cities and connecting people with nature.