The size of firms matters. Even if in every developed economy the majority of firms is small or very small, and even if most labour is usually employed in small and medium-sized enterprises, an important part of production takes place in large firms and a very large proportion of R&D is also carried out within large firms. Large firms are an essential factor in driving and coordinating the work of many smaller firms which are their suppliers or customers. Moreover, large firms represent a specific environment in terms of relations between employers and employees. We can say that any thriving economy needs both a certain number of large and medium-to-large enterprises and a much greater number of small and medium-to-small enterprises. This Section investigates the importance of size in business.