I imagine you could find whole books written on this topic but here are my thoughts. A “startup” may mean different things to different people and depending on the phase, I’d define one as a company that is either pre-revenue (phase 1) or that has revenue but isn’t yet profitable (phase 2). As far as the difference with established corporations, the two distinctions that jump to mind are specialization and uncertainty. Specialization: As a start-up, there’s usually a small(er) team with widely varied functional responsibilities as the company works to get to market. A founder may be operationally responsible for finance, sales, product development, marketing, etc., and also be responsible for sweeping the floors at the end of the evening. In later stage companies, employees are more functionally specialized. Uncertainty: Uncertainty is pervasive in startups in a way that is incomparable with established companies. While established corporations must continually innovate to remain competitive, innovation is usually incremental whereas the very premise of a startup may be based on one or two innovations that the founders and employees of the company are working to validate so the company can survive and hopefully, thrive.