Severals processes exist today for manufacturing colloidal systems of nanospheres or nanocapsules. These nanoparticles have applications in various industrial fields such as cosmetic, pharmacy, food industry, agrochemicals.... The formation of nanoparticles allows the protection of an active molecule by a polymeric coating and the release of this product following a perfectly defined profile, which depends on the nature of the polymer, the type of particle and the field of use. The purpose of this article is to expose the different methods of preparation of nanoparticular systems. These methods are classified in two mains categories. The first gathers most of the methods which are based on polymerization reactions, the second presents the use of preformed polymers (of natural or synthetic origin). A thorough study is devoted to the mechanisms of formation, in order to find the advantages and the disadvantages of each technique to support the development of manufactoring processes.