World-line quantum Monte Carlo methods are reviewed with an emphasis on breakthroughs made in recent years. In particular, three algorithms -the loop algorithm, the worm algorithm, and the directedloop algorithm -for updating world-line configurations are presented in a unified perspective. Detailed descriptions of the algorithms in specific cases are also given.KEYWORDS: quantum spin system, Heisenberg model, quantum Monte Carlo, XY model, XXZ model, cluster algorithm, loop algorithm, worm algorithm, directed-loop algorithm, world-line method