Electronic theories of bonding considers the increase of electron density between two charge centres leading to bonding. A proton may lead to bonding if it is interposed between two filled orbitals. The system should be termed a 'proton bond' although it is not similar to an electron bond. Both σ and {nand} type proton bond formation can be considered. Association of water and formation of bifluoride ion are easily explained in the light of this concept. Proton bond involving a delocalised {nand}-system would make the bonded proton mobile and electrolytic conductivities of water and of solid isopolyniobic acid are explained in terms of mobile protons in delocalised {nand}-system. © 1983.