The new operational mode of aperture-masking interferometry was added to the CONICA camera four years ago. Over the years, the masks - pieces of metal only two centimetres wide - have opened an unprecedented observational window for the NACO instrument. In comparison to the full aperture, they deliver superior point source function calibration, rejection of atmospheric noise and robust recovery of phase information through the use of closure phases. In the resolution range from about half to several resolution elements, masking interferometry sets the benchmark for the present state of the art worldwide in delivering high fidelity imaging and direct detection of faint companions. The technique and observational applications to imaging of circumstellar discs and exoplanets are outlined.