This dissertation focuses on the formation, growth and discontinuance of business populations and firms in Sweden during the 20th century. It addresses some key issues in the domain of economic and social sciences, and in particular entrepreneurship and small business research: if and when firms grow, stagnate and decline, as well as how long firms survive and when they are likely to disband. Previous research has primarily analyzed these questions from a short time frame. Further, an individual or firm-oriented focus is commonly assumed. In that, alternative or complementary explanations to the growth and survival of firms may be disregarded. In contrast to much previous research, this dissertation assumes a micro-to-macro, longitudinal and demographic population approach. The period of investigation is over one hundred years. In addressing the growth and survival of firms, it takes into account the impact of firm-specific structural factors (such as firm age and size), generation (cohort) effects, as well as the influence of macroeconomic, exogenous factors. Further, the relationship between managerial/ownership succession and firm performance is also addressed. Both cross-sectional and longitudinal databases are employed in the dissertation. Its main empirical material consists of unique longitudinal data on new business firms, traced at the firm level from their birth to their termination. More specifically, seven birth cohorts – generations – of approximately 2,200 firms founded in 1899, 1909, 1912, 1921, 1930, 1942 and 1950 are included. The main findings show that ownership/management succession in firms had a quite weak correlation with firm performance and survival. At least at an aggregate level, and with some exceptions, it is debatable if the loss and replacement of owner-managers in small and in larger firms have any observable effects on firm performance. Furthermore, macroeconomic phenomena influence the conditions of individual firms as well as populations/aggregates of businesses. Both the growth and termination of firms and firm populations are found to be related to real economic (environmental) conditions; e.g. favorable macroeconomic conditions implied that firms grew in size. At the same time, under certain circumstances, the influence of structural variables (firm age and size) – as suggested in much previous research – is found to be of importance. As concerns firm growth, as well as firm termination, the economic environment and structural factors interact. These findings challenges individual or firm-level research that mainly focus on personal traits and behaviors in explaining firm success and failure. Other previous assumptions are also challenged when taking a longer time perspective into consideration. For decades, organization and business research have acknowledged a liability of newness and of size for business firms. While this might be true under some conditions, this liability of newness is falsified in the study: the termination behavior of some firm generations did not correspond with these assumptions. Thus, the perspectives and methodology applied in the dissertation complement earlier approaches in entrepreneurship and small business research.