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 systems thinking 1.0, as an integrated whole, embodied in its assembled components, their interactions with each other and the environment. This systems thinking 1.0 defining a system possesses one cardinal deficiency. The deficiency comes from that it does not demand 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 systems behavior together. In other words, integration of systems structure and systems behavior results in the integration of a whole system. Since systems thinking 1.0 does not demand 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, systems thinking 1.0 is weak in defining a system appropriately. Structure-behavior coalescence (SBC) provides a sophisticated way to integrate the systems structure and systems behavior of a system. A system is therefore redefined, by systems thinking 2.0 (architectural thinking), as an integrated whole, through structure-behavior coalescence, embodied in its assembled components, their interactions with each other and the environment. Systems thinking 2.0 uses the SBC architecture description language (SBC-ADL) to formally define the essence of a system and its details at the same time. SBC-ADL contains six fundamental diagrams: a) architecture hierarchy diagram, b) framework diagram, c) component operation diagram, d) component connection diagram, e) structure-behavior coalescence diagram, and f) interaction flow diagram. Since systems thinking 2.0 demands the integration of systems structure and systems behavior, definitely it is able to form an integrated whole of a system. In this situation, systems thinking 2.0 is fully capable of defining a system. In this book, we shall dwell on systems thinking 2.0 through the application of SBC-ADL. By this book's introduction and elaboration of SBC-ADL, all readers will understand clearly how systems thinking 2.0 helps us truly define an integrated whole of a system.