Coexistentialism is a comprehensive knowledge system that fosters wholistic and harmonious living. It is a new development in human understanding which proposes that all of existence is in the form of coexistence. Everything is related to everything else, nothing exists in isolation. There is an inherent harmony and balance in existence and everything in nature is complementary and mutually enriching each other. In order for us to be in harmony and balance within and with all, we need to understand coexistence and live accordingly. Knowledge of existence and knowledge of self (‘I’) leads to knowledge of humane conduct (how to live in harmony with human beings and all of nature). Living with humane conduct is the foundation for actualizing harmony and sustainability on Earth.