This chapter demonstrates the mental health benefits of nature-based solutions in cities. First, factors that determine urban mental health and adverse health effects of environmental stressors in cities are explained. Second, it is demonstrated that green spaces as nature-based solutions for many societal challenges provide co-benefits for mental health by reducing these stressors. It is further discussed how nature-based solutions may target supporting mental health by providing resources for human–nature interaction, enhancing social interaction and strengthening mental resilience. Nature-based interventions that are originally intended to support persons with psychiatric illness are introduced as models for the design of mentally supportive cities. And third, two case studies illustrate the mental health benefits of urban parks with the example of Leipzig, Germany and of street trees by the example of Hyderabad, India. The two case studies were used as application cases for a recent conceptual framework as a guide for putting science into practice.