The global trend of searching for ecologically friendly, ‘green’ chemical processes manifested itself in the chemistry of carbon nanomaterials, in particular, in the development of techniques for their chemical (both covalent and noncovalent) modification. Our effort in this area was focused on two aspects: (i) the development of totally solvent-free (mainly covalent) functionalization techniques; (ii) an attempt to apply our solvent-free approach to different nanocarbons. We designed a series of simple and fast functionalization protocols based on thermally activated reactions with compounds stable and volatile at 150-200 °C under normal or reduced pressure. In most of these protocols not only the reactions take place at a high rate, but also excess reagents are spontaneously removed from the functionalized material, therefore making unnecessary its purification. The main classes of reagents are amines and thiols (including diamines and dithiols), which can be used in conjunction with fullerenes, single-walled and multi-walled carbon nanotubes, as well as nanodiamond. In the case of diamines and dithiols, reactions of the second functional group can give rise to cross-linking effects, or be employed for further derivatization steps (e.g., deposition of metal nanoparticles).