The authors demonstrate in this essential guide how an internal control system (ICS) can make a significant contribution to financial management, particularly in small and medium-sized enterprises. Numerous concrete examples and practical solutions illustrate how an ICS can be implemented pragmatically and beneficially. In the financial sector, it is an indispensable element of good corporate governance, regardless of the legal situation. A well-designed ICS represents an effective management system that supports efficient operational planning and management of the financial area. It contributes significantly to the management and control of liquidity, enhances the efficiency of financial processes, and ultimately supports sustainable business growth.