Convenient synthetic procedures for making nanoparticle latexes with particle diameters in the 12-20 nm range are reviewed. These procedures yield latexes that are more concentrated (20-30 wt. %) and have much less surfactant (8-15 wt. % of the monomer) than earlier procedures. Common acrylic and styrenic monomers, including cross-linkable monomers, can be used. Nanoparticle latexes have properties that are quite different from those of conventional latexes in at least four ways. (1) Their very large surface areas affect particle properties, (2) in some cases the polymer molecules are constrained within particles whose diameters are less than half the root-mean-square diameter of the same molecule in a larger particle, (3) if starved for surfactant, they can form gels in which the particle structure is largely intact, (4) in some cases the tacticity of the polymers is different from bulk polymers. These differences suggest unique applications.