A detailed review is made for the mechanism of gold+sulfur sensitization. Silver-gold sulfide AgAuS isformed more rapidly than silver sulfide by decomposition of labilesulfur compound in gold +sulfur sensitization. Silver-gold sulfide speck promotes theformation of silver sulfide especially at (100) surface in providing decomposition site, and then size distribution of the silver sulfide specks becomes moreuniform than that bysulfur sensitization. There are not so many experimental results supporting that gold atom speck acts as sensitizing center. Two main photographic actions are present atgold+sulfur sensitization, one is electron trapping and the other is gold latensification. Not gold atom speck nor gold-silver sulfide speck but silver sulfide speck acts as electron trap. Characterisity of silver sulfide speck depends on their size, and as the onesformed ingold+sulfur sensitization have more uniform size distribution, almost all specks have a good characterisity for electron trapping. Since latent image specksformed ingold+sulfur sensitized emulsion contain gold atom, minimum size for developability becomes small. There are some other actions for sensitization but they are not so important.Gold+sulfur sensitization has many ways for sensitizing action and the high sensitivity is owing to its complexity.