This International Standard provides guidance on a Petri net based methodology for dependability purposes. It supports modelling a system, analysing the model and presenting the analysis results. This methodology is oriented to dependability-related measures with all the related features, such as reliability, availability, production availability, maintainability and safety (e.g. safety integrity level (SIL) [2] related measures). This standard deals with the following topics in relation to Petri nets: a) defining the essential terms and symbols and describing their usage and methods of graphical representation; b) outlining the terminology and its relation to dependability; c) presenting a step-by-step approach for 1) dependability modelling with Petri nets, 2) guiding the usage of Petri net based techniques for qualitative and quantitative dependability analyses, 3) representing and interpreting the analysis results; d) outlining the relationship of Petri nets to other modelling techniques; e) providing practical examples. This standard does not give guidance on how to solve mathematical problems that arise when analysing a PN; such guidance can be found in [3] and [4]. This standard is applicable to all industries where qualitative and quantitative dependability analyses is performed.