This open access book goes into the details of the characteristics of scale-ups, touching upon various theoretical perspectives (stages of growth models, the role of intangible capital, the tradeoffs between fixed costs and marginal costs) relating to firm growth, to provide a clear definition of this emerging concept. Given the disproportionately large economic contribution of a small number of fast-growing firms, there has been growing interest in a category of dynamic ventures called "scale-ups". The term was popularized by Silicon Valley Venture Capitalists before receiving attention from academics and public policy makers. However, there remains considerable confusion regarding what a scale-up actually is. This is an open access book.