Protein hydrolyzates are commonly used in high-tolerance or hypoallergenic formulas. The relation between the physicochem. properties of hydrolyzed proteins (i.e., size, mol. weight distribution, charge, hydrophobicity), and their emulsifying properties is not fully understood. In this work, the emulsion forming ability (i.e., the equilibrium between droplet formation and coalescence during emulsification), the gravitational stability, the adsorption kinetics and the interfacial dilatational rheol. of whey proteins and whey protein hydrolyzates were investigated. More extensive hydrolysis resulted in a progressive decrease of the surface hydrophobicity of the emulsifiers (i.e., whey protein or whey protein hydrolyzates). Whey protein was able to form smaller emulsion droplets at low concentrations (<1 wt%) compared to whey protein hydrolyzates (WPH). When the concentration of WPH was in excess (>2 wt%), similar min. droplet sizes were obtained due to the adsorption of large peptides. Whey protein-stabilized interfaces showed the lowest interfacial tension and ζ-potential, which both increased with increasing degree of hydrolysis. Whey protein produced stronger oil-water interfacial layers (i.e., high dilatational moduli and non-linear behavior) and had higher protein surface coverage compared to WPH. Small whey protein peptides (<5 kDa) formed a weak oil-water interfacial film, which led to unstable emulsions. In whey protein-stabilized emulsions, β-lactoglobulin showed preferential interfacial adsorption over α-lactalbumin. In emulsions containing WPH, large peptides (>5 kDa) were preferentially adsorbed over small peptides. Emulsion phys. stability was strongly influenced by the oil droplet size, and by the formation of an inter-connected viscoelastic film at the oil droplet interface which was observed only for whey protein and peptides with high mol. weight (>5 kDa). These results should be considered when formulating specialized nutrition emulsions.