The best rate for a noisy (communication) channel to transmit data nearly perfectly is called the capacity. The best error correction strategy is optimized over an unbounded domain as the blocklength diverges, yet the capacity for a classical channel to transmit classical data has a surprisingly simple expression, and there is no capacity gain by coding two channels jointly. This talk will focus on how the capacity of a quantum channel to transmit quantum data deviates from most of the classical counterpart. Most notably, we describe how two quantum channels used jointly can have combined capacity much higher than the sum of the capacities of the constituent channels.