How is material invented? Do rules allowing the mastering of its proprieties depending on specific needs exist? Can material, by essence inert, become intelligent?M. Duneau and C. Janot give here the story of materials and show how matter, like in a Lego game, builds itself and which are the rules of its construction. But nothing is simple: the violation of these rules is often at the origin of marvellous properties. Defects sometimes become qualities!M. Duneau is a research director at the CNRS and C. Janot is a professor. Both are specialists of quasi-crystals.