order to satisfy unfulfilled market demand. Baumol Baumol has argued that entrepreneurship can be either productive or unproductive. Unproductive entrepreneurs may pursue economic rents or crime. Societies differ significantly in how they allocate entrepreneurial activities between the two forms of entrepreneurship, depending on the 'rules of the game' such as the laws in each society. David Audretsch Audretsch defines the entrepreneur as the missing link between investment in knowledge and growth. It is the entrepreneur who adds value to scientific discovery. Entrepreneurship capital is then, just as capital and labor in a macroeconomic model, an essential factor of production in the economy. See also Social entrepreneurship Further reading Casson, Mark C. (1982) The Entrepreneur: An Economic Theory, Oxford: Martin Robertson, [2nd. ed., Edward Elgar, 2003] Chen J. (2005). The Physical Foundation of Economics – An Analytical Thermodynamic Theory. World Scientific. Farmer J.D., Shubik M., Smits E. (2005). Economics: The Next Physical Science? Glancey, Keith D., Mcquaid, Ronald W (2000) Entrepreneurial Economics. Palgrave Macmillan. Tabarok A. (2002). Entrepreneurial Economics – Bright Ideas from The Dismal Science. Oxford University Press. Vining G.T., Van Der Voort R. (2005). The Emergence of Entrepreneurial Economics. Elsevier. Vogel J.H. (1989). Entrepreneurship, Evolution and the Entropy Law. The Journal of Behavioral Economics. Vol. 18, No. 3. Sharma, Vivek, Workbook on Entrepreneurship (2005), Abza Publications, India Parker, S. C. (2009). The economics of entrepreneurship. Cambridge University Press. Nightingale P., Coad A. (2013). Muppets and Gazelles: Political and Methodological Biases in Entrepreneurship Research, SPRU Working Paper Series 2013-03, SPRU - Science and Technology Policy Research, University of Sussex. References Entrepreneurship