This paper explores the potential contribution of trees and forest to the mental wellbeing of diverse populations in Britain. We use a conceptual framework that makes a distinction between three different levels of engagement: everyday life; green health promotion; and green therapeutic care. We then use researched and evaluated case studies in Britain to provide examples associated with these three levels of engagement. The case studies illustrate that practical approaches and interventions are developing rapidly in the Britain. Finally we discuss the main pathways and mechanisms that link mental health and wellbeing and trees and forests. We outline that there are limitations to the current international evidence base and call for consistent approaches within and between countries using a range of methodologies to capture the nuances of the complex relationships between trees, forests and mental health and wellbeing.