The relationship between medium-sized enterprises and banks has changed significantly in recent years. This is primarily due to the reorganization of banking supervisory regulations. The focus of both scientific and practical discussions is, among other things, the question of what opportunities arise for medium-sized enterprises as banks serve as critical counterparts, uncover weaknesses within the companies, and contribute new aspects to decision-making. Mascha Sorg analyzes whether and how banks can fulfill a function that ensures rationality for medium-sized enterprises. Based on a well-founded survey of 332 medium-sized entrepreneurs in Germany, she demonstrates how such a rationality-assuring influence of banks affects the quality of management.