This chapter develops a theory of sustainable enterprises, sustainable enterprise theory (SET), which can only be a valid theory if knowledge about life and nature is complete. Knowledge limitations should not stop enterprises from doing business with a goal of better long-term life on earth. Life demands stewardship of the resources used during one’s lifetime. This chapter develops a model influenced by enterprise theory and resource theory that includes more than money in the business activities of an enterprise. The SET model is used in analyses of accountability, management and in discussions about sustainable business organizations activities.