AbstractFluid‐fluid interfaces containing surface‐active agents or macromolecules exhibit interfacial shear viscosity phenomena. The purpose of this paper is to investigate theoretically the dynamics of liquid‐liquid and liquid‐gas interfaces containing surfactants, and to establish the validity of the proposed model from shear flow data at uncontaminated interfaces.A theoretical analysis for the measurement of interfacial shear viscosity at liquid‐liquid interfaces with an improved viscous traction surface viscometer is presented. The analysis takes into account the finite depths of the two liquids and permits interpretation of the experimental results in terms of interfacial shear viscosities at the liquid‐gas interface in addition to the liquid‐liquid interface. Results of the present analysis clearly show a strong coupling of interfacial and bulk fluid flows.Extensive measurements of the interfacial velocities at a xylene‐water interface were made. A cetane‐water interface was also studied. Interfacial flow data for uncontaminated systems were found to be in excellent agreement with theory.