Abstract <p>Heterogeneous catalysis plays a pivotal role in many key chemical transformations engaged in industrial productions of commodities and fine chemicals, environmental protection and renewable energy technologies. With the aim at overcoming limits dealing with the use of benchmark precious metal-based catalytic materials, metal-free carbon-based systems (eventually doped with light hetero-elements) and 2D transition metals dichalcogenides (TMDCs) have gained increasing interest among the scientific community as effective, cheap and sustainable catalysts for several challenging transformations. However, their complex structural/chemical composition poses often serious limits to the identification of the active sites engaged in the processes hence hampering any rational optimization of their performance. On this ground, chemical functionalization with well-defined moieties holds the potential to tackle these issues through a controlled engineering of surface chemico-physical/structural properties of either organic or inorganic materials. In this work, achievements in (electro)catalytic processes promoted by covalently grafted materials will be described, highlighting at the same time the key role of this <i>top-down</i> synthetic strategy in the comprehension of key structure/reactivity relationships as well as the underlying reaction mechanisms.</p> Graphical abstract <p></p>