Synthetic biology depends on technologies for reading and writing DNA sequences of genes. Modification is almost always done at the genetic level because genes are heritable, needing to be engineered only once. ‘How synthetic biology is done’ describes the processes of sequencing DNA and DNA synthesis. Sequencing DNA is important for two main reasons: to analyse natural genes and natural gene-controlling regions of DNA; and to verify the correctness of DNA we have tried to write. The design of synthetic constructs is also considered along with the use of synthetic biology libraries; how the synthetic system is loaded into a living cell; and the potential issues of cross-talk and orthogonality.