This thesis reviews historical attempts to utilize nature therapeutically, and then examines whether expanded understandings of the interconnections between human’s environments and health support the utilization of nature exposure therapies in mental health practice. Incorporating research from an array of disciplines, I focus on the health impacts of human’s non-visual photoreceptive systems as well as human associated microbial ecosystems. The ubiquity and extent of human alterations to our light environment and the apparent links between exposure to altered light regimens and mental health issues indicate a need for both further research and immediate action. Despite an incomplete understanding of the full impacts of light on mental health, the research presented in this review indicates the need for widespread utilization of lighting design which accounts for the health impacts of light. Such design generally aims to more closely replicate sunlight’s natural rhythms of light spectrum, timing, and intensity. Recent advances in the genetic sequencing of microbial populations have opened a powerful lens for researchers to examine the vast complexity of human associated microbial populations. The research has greatly expanded understanding of the critical roles co-evolved microbes play in human health. Gut microbes are increasingly seen as the mediators of the human gut-brain axis, interacting with human’s genes and environments, to influence and be influenced by our mental states. The tight linkages indicate to many researchers the therapeutic potential of interventions targeting microbial populations in the human gut. Research utilizing increasingly advanced genetic sequencing methods continues to unravel the complex interactions between human hosts, their microbiomes, and their states of health and/or disease. This thesis argues that future research into connections between microbes and mental health should include high-quality studies of existing therapeutic interventions which involve contact with nature and may already be taking advantage of this potential.