The functional and interfacial properties of beta-casein and dephosphorylated beta-casein (DeP beta-casein) were studied at pH 7.0 in 10 mM phosphate buffer. A decrease in emulsion stability and an increase in foamability was observed. Results from a variety of interfacial techniques including electrophoretic mobility, thin film thickness, surface and interfacial tension, surface rheology, adsorbed layer thickness, and adsorption isotherms of dephosphorylated beta-casein and beta-casein are reported. The results demonstrate that the phosphorylated groups of the N-terminal region of beta-casein are important for stabilizing emulsions. This is either as a direct result of charge repulsion between beta-casein N-terminal regions or more probably as an indirect result of the reduced N-terminal charge permitting DeP beta-casein to adopt a different interfacial conformation resulting in a loss or reduction of a steric barrier.