What are firms?

"We study how firm characteristics evolve from early business plan to initial public offering to public company for 49 venture capital financed companies. The average time elapsed is almost 6 years. We describe the financial performance, business idea, point(s) of differentiation, non-human capital assets, growth strategy, customers, competitors, alliances, top management, ownership structure, and the board of directors. Our analysis focuses on the nature and stability of those firm attributes. Firm business lines remain remarkably stable from business plan through public company. Within those business lines, non-human capital aspects of the businesses appear more stable than human capital aspects. In the cross-section, firms with more alienable assets have substantially more human capital turnover"--National Bureau of Economic Research web site.