Purpose – The purpose of this paper is to clarify the distinctions and complementary of William Baumol and Israel Kirzner’s classifications of and insights into entrepreneurship, and thus providing a more complete taxonomy of the substance of entrepreneurial activity. This paper also attempts to clarify distinctions between unproductive and destructive entrepreneurship. Design/methodology/approach – This paper illustrates a more complete taxonomy of the substance of entrepreneurial activity by examining entrepreneurial innovation in drug markets both legal and illegal, identifying cases of productive, unproductive, superfluous, erroneous, destructive, and protective entrepreneurship. Findings – This paper finds that the classifications of entrepreneurship (productive, superfluous, unproductive, erroneous, protective and destructive) put forth by Baumol, Kirzner, and the institutional entrepreneurship literature are complementary. While Baumol seeks to explain the disequilibrating tendencies of entrepreneurship, Kirzner seeks to explain the equilibrating tendencies of entrepreneurship within the institutional context. Originality/value – This paper utilizes case studies from legal and illegal drug markets to uniquely and better explain the six cases of entrepreneurship. This paper also contributes to the literature by clearly articulating the complementarity of Baumolian and Kirznerian entrepreneurship.