[en] Crystal surfaces, and more particularly semiconductor and oxide surfaces, are of great interest for both technological applications and fundamental physics. As a consequence, they have been intensively studied in recent decades and now their control at the atomic scale has been achieved. It is thus possible to go to next step and look at the interaction of these surfaces with specific atoms or molecules to improve or change their properties. In this topical review article, we describe in detail some selected examples of modifications of the electronic properties of semiconductor and oxide surfaces that can be expected with the adsorption of atoms such as hydrogen, alkalis or noble metals. By selecting an appropriate adsorbate on a specific substrate the electronic properties can be tuned to match desired characteristics. (topical review)