Several recent reviews have concluded that, while certainly not a panacea, exposure to nature and outdoor activities can improve mental health for at least some symptoms, causes, patients, and circumstances (1–6). They are particularly relevant for the psychological components of chronic disease syndrome, namely depression and dementia (7–9). Outdoor exercise plays a role, in addition to outdoor environments (10–12), but nature-based outdoor activities yield benefits additional to those of exercise alone (13–17). Outdoor therapies can also assist in overcoming some types of chronic pain (18). They are valuable at all ages, from children (19, 20) to seniors (21, 22), and for those with both minor and severe clinical symptoms (23). All of these have substantial economic implications (6, 24, 25). Currently, however, outdoor therapies have limited deployment, especially in wealthy urbanized nations where they are most valuable. Government health agencies, and private health insurers, run educational and marketing campaigns, but these are for voluntary patient-funded activities. There are various school and youth adventure education programs (19, 20), but these are preventive rather than therapeutic. A few countries have trialed so-called green prescription programs (26), but too small and short to be effective. Some privately run programs may be more successful (27), but they are targeted to specific market sectors, unconnected with mainstream health care. None of these yet provide for routine diagnosis and prescription of outdoor therapies, for patients who present themselves at their general practitioners with mental health concerns. Here, therefore, we consider what additional research may be required to achieve this. There are both social and technical aspects. The key social obstacle is that outdoor therapies are not yet perceived as mainstream medicine. Even though the practical delivery of outdoor therapies is very similar to widely prescribed physiotherapies and psychotherapies, outdoor therapies are not yet available through publicly or insurance-funded medical diagnosis, prescription, and providers. They are offered principally by private providers, who are forced to adopt business and marketing models more closely aligned to discretionary activities such as the fashion and beauty industry. Historically, similar social obstacles were also faced, and overcome, by many other components of modern health-care systems. It takes time, institutional change, and technical information for them to become routine (1, 6). Here, we focus on the technical obstacles and the research required to overcome them. Recent reviews agree that knowledge of the therapeutic links between nature exposure and mental health is currently only at proof-of-concept stage, and research is now required to elucidate dose–duration–response relationships (1, 4, 6). We endorse this view and propose two additional areas of research. The first additional area is to differentiate (a) patient symptoms and personality traits and (b) characteristics of therapies, to prescribe specific therapies that match particular patients and conditions. The second is to test the social levers needed to persuade individual patients to adopt and follow through with courses of outdoor therapies once prescribed.