Exceptionally smooth glass, vitreous silica and metal surfaces are required for a variety of purposes in industrial and scientific laboratories. A variety of defects may mar the perfection of an optically polished surface. In a supersmooth surface, significant imperfections may have heights of about 1 nm and the principal defects which are difficult to eliminate are sleeks and fine undulations. No single method of assessing surface quality has adequate sensitivity to characterise all types of defect and the instruments and inspection techniques employed include optical microscopy, optical scatter and interferometry, bire-fringence, ellipsometry, electromechanical stylus, electron microscopy and X-ray scatter and reflection. The ability to detect and measure surface imperfections of atomic dimensions may enable the origin of the defect to be traced. In this way polishing technology may be improved systematically, in contrast to the traditional empirical approach.