In this chapter, we introduce a highly expressive, self-contained reflective meta-model of object-process methodology (OPM). OPM enables universal system modeling based on the notions of processes that transform objects. Extending the object-oriented approach, which views processes as residents of objects, OPM provides for the existence of stand-alone processes that can represent transformations in complex systems such as businesses, aircrafts or organisms. A system modeling and development methodology, which is a combination of a language for expressing the universal (or domain) ontology and an approach for developing systems that uses this language, can be expressed in OPM using objects, processes and links among them. Through the reflective OPM meta-model, we demonstrate the expressive power of OPM and its applicability as a universal tool for architecting systems that involve structure and dynamics in a highly, intertwined manner.