Schematic evolutionary diagram proposed for the formation of high-mass stars. (1) Massive filaments and spherical clumps, called ridges and hubs, host massive dense cores (MDCs, 0.1 pc) forming high-mass stars. (2) During their starless phase, MDCs only harbor low-mass prestellar cores. (3) IR-quiet MDCs become protostellar when hosting a stellar embryo of low mass. The local 0.02 pc protostellar collapse is accompanied by the global 0.1−1 pc collapse of MDCs and ridges/hubs. (4) Protostellar envelopes feed from these gravitationally-driven inflows, leading to the formation of high-mass protostars. The latter are IR-quiet as long as their stellar embryos remain low-mass. (5) High-mass protostars become IR-bright for stellar embryos with masses larger than 8 M_⊙. (6) The main accretion phase terminates when the stellar UV field ionizes the protostellar envelope and an H ii region develops.