Systems tend to be very complex. Modular approaches therefore provide the only basis for efficient solutions of today and the future. Modular approaches require well defined standard interface, especially if standard products supplied from third parties are considered to be integrated into the system for further cost effectiveness.These ideas are considered to be the guidelines for application systems' design as well as for tester systems. The following paper focuses on test systems especially. A generic model, taking into account the various constraints for tester applications, describing a “lean” modular architecture is derived. The todays achievements and the directions into which further efforts for enhanced tester design must go are highlighted: Provide sufficient interfaces for efficient access to system under test. Provide generic (tester) module interfaces for optimal modular design and easy integration of third parties' modules.