Based on the evaluation of a wide variety of experimental results a new model on the nature of spilt-over hydrogen (H*) is proposed. The adsorbate (H*) - solid interaction is incorporated into the description of the state of activated hydrogen. The H* species are considered as electron donors located at the surface. This supposition results in a coexistence of H atoms and H+ ions. The ratio of these species is determined by the electronic properties of the uniform system adsorbate/solid. The new model is applied to interpret various experimental results on hydrogen spillover. Furthermore, the consequences of the new model claiming a dynamic equilibrium of two spilt-over species on their spectroscopic observation are discussed.