A method for monitoring a polishing condition of a surface of a wafer in a polishing process is provided, the method comprising the steps of providing a wafer (16) to be polished, the wafer (16) having at least one optically distinguishable feature (20) below a transparent or translucent layer (22) to be polished; selecting one or more of said features (20) for monitoring; measuring an optical contrast profile (62; 72; 82; 92) across one or more of said selected features (20); determining the polishing condition of the surface of the wafer (16) on the basis of the measured contrast profile (62; 72; 82; 92); and repeating the steps of measuring the optical contrast profile (62; 72; 82; 92) and determining the polishing condition until a predetermined polishing condition is reached. The invention also provides a method for polishing wafers by a CMP polishing tool and apparatus for monitoring a polishing condition of a surface of a wafer (16) in a polishing process.