SummaryThe properties of adsorbed films of αs1-, β- and κ-casein and sodium caseinate are compared at the planar oil–water interface, at the surface of emulsion droplets, and at the surface of polystyrene latex particles. Attention is directed towards understanding (i) the relationship between the molecular characteristics of the caseins and their surface activities and surface viscosities at the oil–water interface, (ii) the nature of competitive adsorption between the caseins (particularly αs1- and β-), and (iii) the effect of Na and Ca ion concentrations on electrophoretic mobilities and flocculation behaviour.