Functionalized polymer colloids were synthesized by emulsion polymerization having specific ionic groups on surface. In this review, a comprehensive study on the synthesis of functionalized polymer colloids is carried out. Monodisperse polymer colloids with acetal, aldehyde, chloromethyl, and amino functionalities were synthesized by a multi-step emulsion polymerization process. In the first step, the seeds were synthesized by batch emulsion polymerization of styrene; and in the following steps, onto the previously formed polystyrene latex particles, the functional monomers were co- and/or ter-polymerized. Some of the synthesized latexes were chosen as the polymeric support to carry out the covalent coupling with a protein and to test the utility of the latex-protein complexes formed in immunoassays. In addition, the colloidal stability of polymer colloids is theoretically and experimentally analyzed. This study shows that classical DLVO (Derjaguin, Landau, Verwey, Overbeek) theory can explain the stability of weakly charged polymer colloids. This is not sufficient in the case of highly charged polymer colloids using hydrophilic monomers. In such a system, the steric repulsion is not negligible and an electrosteric repulsion mechanism must be considered. Our interest has centered on studying this effect from a quantitative point of view. Although the method used contains five variables, it is possible to considerably reduce this number if some of them are calculated by alternative methods (ψd, δ) or taken from literature (A, x).