While we first learned about cellular regulation by molecular networks nearly 50 years ago, synthetic biology as a field has emerged in just the last 15 years. The rise of high throughput biology, advances in DNA sequencing and synthesis, understanding of gene regulators and sensors, and the development of computational models and logic, have enabled the birth of a new area of science with tremendous promise and many potential applications. Scientists now have the ability to write genetic code or sequences to build biological systems, new living organisms programmed with specific functions. Already, designed or engineered bacteria have contributed to significant advances in agriculture and biofuels.