The Interfacial Rheology System combines the outstanding and well-established properties of a Physica MCR rheometer with a newly developed interfacial rheology cell based on a bi-cone geometry. This bi-conical disk rheometer allows the measurements of steady state and transient interfacial shear viscosities as well as elasticity properties of interfacial films and layers. The use of a research rheometer extends the range of standard rheological test methods like flow curve, creep and creep recovery, stress relaxation or oscillatory measurements which are common in three-dimensional bulk rheology to the rheology of two-dimensional interfaces. The sensitivity of the Physica MCR rheometer at low torques gives the opportunity to investigate interfacial films with very low viscosities. It even extends the application range of the biconical geometry, which was thought to be exclusively for measurements at liquid/liquid interfaces, to rheological experiments on layers at the air/water interface. The influence of the bulk phase contribution is taken care of by a full hydro-dynamical analysis of the flow field for a bi-cone geometry allowing a quantitative determination of the relevant interfacial rheological properties.