Optically transparent sound absorbers made out of micro-perforated structures were introduced 20 years ago. In between various applications and developments have been conducted. In this paper lighting sound absorbers or sound absorbing daylight ceilings as well as fully transparent absorbers in front of glass facades are discussed. Representative sound absorption data for different set-ups are presented. Metal, wood, polycarbonate plates and foils as well as other sheet materials have been micro-perforated. A short review of the applications of various different materials with transparent micro-perforated sound absorbers is given.