Abstract The preparation of silver halide grains in photographic emulsions is one of the most important technologies for the development of new silver halide photographic materials with high capability, and significant progress has been made over the last decades to make silver halide grains controllable with respect to size, shape, halide distribution, and crystal defects. Monodispersed silver halide grains with sophisticated structures are being developed. In this chapter, descriptions are focused on the structure and mechanism of the formation of these grains.