Firms are one of the main characters of any economy and an excellent observatory for monitoring a nation's evolution. The history of Italy's productive system in the last 150 years is divided into three parts, corresponding to a similar number of industrial revolutions. While firms obtained excellent results in the first two, their inability to grow further inhibited the wide use of the Third Industrial Revolution's features, information and communication technologies. This became a serious obstacle for Italy reaching the international economic frontier. There are many causes-political and economic, macro and microeconomic, domestic and international-behind the turnaround in Italy's economic performance, but the key one was firm size. The argument is developed along three steps. First: firm size is positively correlated to innovation, internationalization, adoption of advanced technologies, and ability to face new competitive challenges; larger firms record higher productivity both in levels and growth rates. Second: the distribution of firms in terms of dimensions was adequate until the 1970s, but defective later on. Finally: because firm size is not a given (but an endogenous choice of entrepreneurs), this chapter examines some key entrepreneurs and managers so as to identify the main features of Italian entrepreneurship.