Formation of multicomponent layers via electrografting of aryldiazonium salts has been recognized by materials scientists and electrochemists as a powerful tool due to their high capability for covalent surface modification with multiple functionalities. The past decades have seen significant progress in fabrication and application of surfaces decorated with layers containing more than one component, so called mixed layers. This progress is based on advances in the understanding of aryldiazonium salt-based electrochemistry and their surface chemistry properties. In this critical review, we summarize the different strategies for controlling formation of the mixed layers, especially with respect to surface composition, spatial distribution and surface morphology whereupon the focus shifts to the diverse range of applications in which mixed layers are employed. The limitations of existing strategies and perspective opportunities will also be presented. (C) 2016 Elsevier B.V. All rights reserved.