The objectives of synthetic biology include to understand life through synthesis and to engineer complex biological systems based on general principles of modern engineering sciences. The engineering goal relies on the availability of molecular parts with diverse functions that can be predictably integrated, regulated and reused. These parts may include proteins, RNA, DNA and their complexes. Based on the understanding of molecular mechanisms and judicious combinations of rational design and laboratory evolution, specific interactions, regulatory functions and activities of biomolecules can be artificially changed or created. This comprises an important strategy to artificially regulate and reprogram existing biological systems. It also lays the foundation for the bottom-up design and construction of artificial biological systems of increasing complexity.