Humans have evolved in a microbe-rich environment and have become dependent on some of these microbes to colonise us, provide essential chemicals, and prime our immune systems. In many urbanised, western countries, there has been a loss of contact with these biodiverse environmental microbiota, which might be associated with the increased burden from diseases such as asthma, allergies, and autoimmune disorders. Here we summarise our growing understanding of the relationship between exposure to biodiverse environmental microbiota and their potential to provide health benefits. We start by covering the known range of health outcomes associated with green space exposure and then explore the possibility that these benefits are mediated by microbes. We provide evidence to support the notion that environmental microbiota influence the human microbiota and that this in turn leads to a range of health effects. The evidence is strong enough to recommend biodiverse green space exposure both as a clinical and as a public health intervention and discuss what types of environments might be most suitable to recommend. To maximise potential health benefits, we need to improve both the quantity and quality of green spaces and ensure that these are accessible to those communities that stand to benefit most.