Synthetic biology brings engineering tools and perspectives to the design of living systems. In contrast to classical cell engineering approaches, synthetic biology enables cellular networks to be understood as a combination of modular elements in much the same way as unit operations combine to describe a chemical plant. Consequently, models for the behavior of these designed systems are inspired by frameworks developed for traditional chemical engineering design. There are direct analogies between cellular metabolism and reaction networks in a chemical process. As examples, thermodynamic and kinetic models of chemical reaction networks have been used to simulate fluxes within living systems and predict the performance of synthetic parts. Concepts from process control have been brought to bear on the design of transcriptional and translational regulatory networks. Such engineering frameworks have greatly aided the design and understanding of living systems and have enabled the design of cells exhibiting complex dynamic behavior and high productivity of desirable compounds. This review summarizes efforts to quantitatively model cellular behavior (both endogenous and synthetic), especially as related to the design of living systems. (C) 2012 Elsevier Ltd. All rights reserved.