 Synthetic and systems biology are sometimes described through the complementary aims of forward and reverse engineering. Forward engineering refers to the design of systems with novel functions, often by drawing on an existing high-level model (e.g., an existing code or living cell). Forward engineering, or re-engineering, can lead to more complex systems, but simplicity may also be pursued through implementation of a more abstract coding language or through reduction or rewiring of (genetic) circuits. Reverse engineering refers to the aim to understand the functioning of a system ‘backwards’ by examining an existing system in contexts where consulting a design protocol is not an option. The search for recurring network motifs  (Section 1.1.1)  is an example of how systems biologists may reverse engineer the structure of a system to understand its functional capacities. Because functional features such as robustness are not only important to the survival of organisms but also to design problems in engineering, reverse engineering of organizational features that underpin such capacities is an important aim in both fields (Csete &amp; Doyle 2002; Hartwell et al. 1999; Kitano 2004; Stelling et al. 2004).