The field of entrepreneurship continues to struggle with the development of a modern theory of entrepreneurship. In the past 20 years development of the current theories of entrepreneurship have centered on either opportunity recognition or the individual entrepreneur. At the same time many theoretical insights have come from economics including a rediscovery of the work of Schumpeter. However because there is a lack of clarity about the theoretical assumptions that entrepreneurship scholars use in their work, assumptions from both individual opportunity recognition and economics have been used as if they are interchangeable. This lack of theoretical distinction has hampered theory development in the field of entrepreneurship. While explanations of entrepreneurship have adopted different theoretical assumptions, most of these concern three central features of entrepreneurial phenomena: the nature of entrepreneurial opportunities, the nature of entrepreneurs as individuals, and the nature of the decision making context within which entrepreneurs operate. Nonetheless, various theoretical traditions in the field have adopted radically different interpretations with respect to these assumptions of entrepreneurial phenomena, therefore arriving at different explanations of these phenomena. Theories of Entrepreneurship investigates two sets of assumption about the nature of opportunities, the nature of entrepreneurs, and the nature of the decision making context within which entrepreneurs operate. It is suggested that these two sets of assumptions constitute logically consistent theories of entrepreneurship. Moreover, these two theories are complementary and can be applied to widely studied entrepreneurial phenomena -- the organization of the entrepreneurial firm. These applications demonstrate both the differences between these two theories and how they can be complementary in nature. Theories of Entrepreneurship sets the basis for future explorations into entrepreneurship theory. Students and researchers alike will benefit from the framework presented by the author in developing the theoretical underpinnings of entrepreneurship.