PROFIBUS diagnosis is a complex matter: Depending on the respective application, diagnosis information is required in various places, in different systems, at varied points in time, in distinct forms and in varying degree of detail. At the same time, PROFIBUS diagnosis is not just limited to physical measurements during commissioning. The valuable diagnosis information can be efficiently used in all phases of the life cycle. Diagnosis concepts already defined in the planning stage not only speed up commissioning and acceptance processes, but are particularly useful in daily operation.