Human beings have employed the notion of systems so widely in all kinds of scientific studies. Systems definition is an artifact created by humans to describe what a system is. A system has been defined, by general systems theory 1.0, as an integrated whole, embodied in its components, their interactions with each other and the environment, and the principles and guidelines governing its design and evolution. This general systems theory 1.0 definition of a system possesses one cardinal deficiency. The deficiency comes from that it does not require the integration of systems structure and systems behavior. Systems structure and systems behavior are the two most significant views of a system. In order to achieve an integrated whole of a system, we first need to integrate the systems structure and behavior together. In other words, integration of the systems structure and systems behavior results in the integration of a whole system. Since general systems theory 1.0 does not require the integration of systems structure and systems behavior, very likely it will never be able to form an integrated whole of a system. In this situation, general systems theory 1.0 is powerless in defining a system. SBC (i.e., structure-behavior coalescence) architecture provides a sophisticated way to integrate the structure and behavior of a system. A system is therefore redefined, by general systems theory 2.0 (general architectural theory), as an integrated whole, using the SBC architecture, embodied in its assembled components, their interactions with each other and the environment, and the principles and guidelines governing its design and evolution. Since general systems theory 2.0 requires the integration of systems structure and systems behavior, definitely it is able to form an integrated whole of a system. In this situation, general systems theory 2.0 is fully capable of defining a system. In this book, we shall detail the general systems theory 2.0 defining a system through the application of SBC architecture. By this book's introduction and elaboration of SBC architecture which covers the: a) evolution&motivation view, b) multi-level (hierarchical) view, and c) systemic view of a system, all readers will understand clearly how the general systems theory 2.0 helps us faithfully define an integrated whole of a system.