The surface modification by organics has been booming over the past twenty years in the context of the development of 2D nanomaterials for a wide range of applications. The diazonium salt chemistry represents a valued approach since it allows the covalent attachment, under mild experimental conditions, of functional moieties to various substrates. The potential of this method can be greatly enhanced by exploiting it to prepare reactive organic layers intended for the coupling of more complex molecular structures. This two-step approach, called ‘‘post-functionalization’’, has been successfully exploited to provide working surfaces for a wide variety of applications such as sensors, catalysis, energy storage or nanoelectronics. This review aims to detail all the chemical coupling methods implemented on modified substrates via the diazonium chemistry (352 references), with an emphasis on the experimental conditions used and on the efficiency of the couplings. An overall table collects the references, classified by coupling method, modified substrate and targeted application.