Publisher Summary Currently, the most widely used photographic system is based on silver halide emulsions. This is believed to be because of some specific properties of the silver halides directly linked with the formation, stability, and catalytic activity of small silver clusters. This chapter provides evidence that the photographic process is not an exceptional sequence of peculiar reactions, the occurence of which is entirely because of some extraordinary properties of silver halides. The results obtained from the present analysis hint already some quite interesting and optimistic conclusions. The basic property of silver halides to form a developable latent image should not be regarded as a wonder. Any photosensitive compound decomposing with reasonable quantum efficiency should be able to build up centers catalytically active for a suitable process of development. The practical sensitivity attained should depend principally on two parameters. The first one is the mobility of the decomposition product on the surface of the host entity, enabling the efficient coagulation into larger individual clusters. The second one is the nature of the development reaction used to intensify the clusters obtained via the primary photodecomposition process.