Amphiphilic latex nanoparticles comprise a core and shell, The core contains hydrophobic vinylic grafted copolymer and hydrophobic vinylic homopolymer, and the shell to which the hydrophobic vinylic polymer is grafted is a hydrophilic, nitrogen-containing polymer. Typically the particles are made by a process which involves generating radicals on the nitrogen atoms of said hydrophilic polymer, and then initiating free-radical polymerisation of said vinylic monomer, hydrophobic vinylic polymer separating to form latexes of highly monodispersed core-shell particles with the hydrophobic polymer as the core and said hydrophilic polymer as the shell.