Petri nets provide a formal framework for system modelingand validation which has proven to be very reliable inpractice. This book presents variousnet models appropriatefor designing specific systems, where systems are understoodvery generally as "organizational systems" in whichregulatedflows of objects and information are significant.The models are interrelated in the sense that they havecommon interpretation patterns: together they can beunderstood as a method for specifying any given system orany section of such a system to any given degree ofrefinement. The simple and immediately understandableprinciples of system modelling with nets makes it possibleto provide an illustrated description of this method withoutgoing into the mathematics behind it. The text is based oncourses the author developed for project engineers andproject managers in the area of embedded computer systems.