‘Trans-Neptunian objects’ looks at the identity and properties of objects beyond Neptune. The compositions of Pluto and Charon are explored, as well as their atmospheres and mineral deposits. The ten largest trans-Neptunian objects are listed, and assumptions about their size explained. What colour are TNOs? Do they have satellites? When will trans-Neptunian objects more distant than Pluto and Charon be investigated? Have we discovered all the large objects belonging to our Solar System? What is ‘Planet X’, and where is it likely to be? What is the Oort Cloud? Do long-period comets come from one particular region of the sky?