Frequently changing machining operations are a characteristic feature in one-off and small batch size production and require a high degree of flexibility in the production processes and facilities. Process monitoring systems applied in such a production environment have to be able to supply reliable process information under varying machining conditions. Therefore, generic and flexible monitoring solutions are needed, adaptable to the requirements of specific machining applications with minimum efforts. In this paper the requirements for such generic and flexible monitoring approaches are critically discussed. In the second part, monitoring strategies for a process state analysis in face milling, end milling and drilling operations is described, adaptable to varying machining conditions by combining several sensing and evaluation methods.