Synthetic biology endeavours to apply engineering principles to the design and construction of new biological parts, circuits and devices. These principles include modularity and standardization of basic biological building blocks, and rational circuit design based on consistent mathematical approaches. While our ability to read (sequence) and write (chemically synthesise) genetic information still far exceeds our ability to rationally design new biological circuits, progress is being made in the implementation of circuits of increasing complexity in living cells. Much can be learnt by an iterative process of design-build-test-modify, even on very simple genetic circuits. In this talk I will give an introduction to synthetic biology, with some recent examples drawn from the literature.