We confine a monodisperse bubble monolayer between the two parallel plates of a rheometer. One plate is fixed and the other undergoes an oscillatory tangential motion, so that the bubbles are sheared. We measure the shear stress as a function of the imposed strain amplitude and frequency. The interfacial shear and dilational moduli of the foaming solutions are studied in independent experiments. Like a 3D foam, the bubble monolayer consists of soap films connected via Plateau borders, but its structure is much simpler, enabling us to study and model the quantitative link between interfacial rheology and the macroscopic mechanical response.