Paul Tillich is exceptional in modern theologians that his distinctive and abundant understanding of the concept of life and spirit has the potential to engage with other disciplines, such as biology, psychology, cosmology and social science; and that his ontological understanding of "life as spirit" which is so crucial in the ecological consideration, is so complex and subtle that enables powerful and critical inter-religious dialogue in environmental ethics. This book argues that, despite the fact that Tillich did not engage in ecological and environmental theology directly, his abundant personal experience of nature-mysticism and intellectual understanding of the idea of nature rooted in his Lutheran and German idealist heritages and, more importantly, his ontological-pneumatological holistic and multi-dimensional conception of unifying and differentiated reality, perfectly and organically coupled with the theonomous vision of theology of culture, nature and morality is profoundly ecologically oriented.