Quantum information is radically different to classical information. For example, it can be negative -- in a sense, after you are given quantum information, you can know less. This can be given a precise operational meaning by quantifying how much quantum communication is needed to transfer part of a quantum state. Another example: two quantum channels, both with a transmission capacity of zero, can be combined to yield a nonzero capacity, something impossible in the classical world. Iíll also discuss applications of quantum information theory to fundamental physics.