The paper represents a structured survey of theoretical and empirical literature about the dependency of efficiency on organizational size. First the main features of the discussion of (dis-)economies of scale are briefly outlined. The main part provides a comprehensive table listing theoretical studies and their controversial arguments as well as a table containing the empirical findings of selected investigations. The final section sums up the most important results. It is argued that first the verdict on size and efficiency cannot be generalized and rather depends on certain economic conditions, second in many cases, however, there exists a (minimum) optimal plant and firm size (the latter at roughly 500 employees) and third the development of the economic environment within the past 15 years has tended to shift the comparative advantages of efficiency from big, dominating, but bureaucratically paralysed to small and highly flexible firms.