Is matter real? Are persons real? Is time real? This Very Short Introduction discusses what, if anything, is "real" by looking at a variety of arguments from philosophy, physics, and cognitive science. Jan Westerhoff shows that the question "what is real?" is not some esoteric puzzle that only philosophers ponder. Scientists also ask this question when they investigate whether candidates for the fundamental constituents of matter are actually "out there" or just a mere abstraction from a successful theory and cognitive scientists ask it when trying to find out which set of the bewildering array of data processed by our brain could constitute the basis for the self.