Quantum error correction and fault-tolerant quantum computers are often informally used interchangeably. To experts the terms have slightly difference meanings. Quantum error correction is a scheme for protecting information from noise in device. Fault-tolerance builds on this. Fault-tolerant quantum computers also prevent errors from spreading during the error correction process or during a computation. It is a richer and broader subject. To build a useful quantum computer, we really do need fault-tolerance and not just error correction. At Riverlane, we are really solving the fault-tolerance problem, but often just call out “quantum error correction” since this phrase is more commonly known by non-experts.