The ability to rationally engineer microorganisms has been a long-envisioned goal dating back more than a half-century. With the genomics revolution and rise of systems biology in the 1990s came the development of a rigorous engineering discipline to create, control and programme cellular behaviour. The resulting field, known as synthetic biology, has undergone dramatic growth throughout the past decade and is poised to transform biotechnology and medicine. This Timeline article charts the technological and cultural lifetime of synthetic biology, with an emphasis on key breakthroughs and future challenges.