Richard Feynman 1 Introduction Synthetic biology is a relatively new but already broadly spread field of research, developing and implementing previously non existing biological molecular tools, devices and cellular structural and functional modules. It has found relevance and a wide range of applications in fundamental and biotechnological research. Existing, repurposed or fully novel, synthetic molecular parts (and circuits) are rationally designed and assembled into biological modules that will perform a previously determined, desired function . Its hallmark is the integration of classical engineering principles into biological research approaches (Figure ). The classical engineering cycle is executed for constructing a given device with desired properties and functionalities. The cycle begins when a user/customer provides a detailed specification of how the product should look like and work. Engineers start a design phase involving the choice and repurposing of preexisting parts, the development of rational guidelines to assemble parts into a device of higher complexity, the generation of a prototype, its testing and evaluation of whether it conforms to the specification. Normally several rounds of this cycle are needed until the product is finished. This iterative strategy has two main requirements: a precise quantitative description of the structure and functionality of the parts or modules used, and the generalised application of mathematical models for the design and evaluation of the performance of the device .