Quantum bits are intrinsically error prone, and thus a powerful quantum computer eventually will need error correction to perform complex computations. Here John Martinis explains the basic concepts behind error correction, showing it fundamentally arises from the anti-commutation relation of the qubit measurement operators, and the commuting nature of pairs of qubits. John Martinis then shows how error correction actually works for the surface code, which presently is the most practical architecture for building a quantum computer.