The concept of machine is fundamental in informatics, but it seems to have never been completely defined. We of course know a few things about machines. We know that computers, robots, networks... are machines. We know that machines are physical objects. We know that machines, in informatics, are computing devices... But this leaves room for many concepts. We shall discuss in this paper how the concept of machine has evolved during the last decades to become broader and broader. This evolution has been triggered by at least two factors: the development of new types of machines and a more fundamental investigation of the limits of computation, when performed by a machine.