The process of miniemulsification allows the generation of small homogeneous, and stable droplets of monomer or polymer precursors, which are then transformed by (as many as possible) polymer reactions to the final polymer latexes, keeping their particular identity without serious exchange kinetics being involved. The main focus of this Review is laid on a detailed description of the working principles of miniemulsions, the examination of the kinetics during the polymerization process, and the generation of different particle structures by appropriate thermodynamic handling. It will be shown that the strength of miniemulsions is the formation of polymeric nanoparticles consisting of polymers or polymer structures, which are not accessible by other types of heterophase polymerization. Non-radical polymerizations and the formation of hybrid materials by the encapsulation of resins, inorganic materials, or liquids are some examples showing the wide applicability of miniemulsions also for technologically relevant questions. With the miniemulsification of molten inorganic materials followed by a reaction, miniemulsions cross the border of polymers and open new possibilities in the fabrication of solid particles for material science.