The state of the art in the use of two probes of the occupied electron states, namely C KVV Auger emission and C 1s photoemission, in the study of a-C and a-C:H is reviewed, with particular attention to the issue of deriving the sp 2 fraction. The local character of the two probes justifies decomposition of the relative spectra into an sp 2 and an sp 3 component. While however decomposition of the C 1s spectrum relies upon a theoretical basis and allows accounting for disorder effects in the amorphous state, no theory is available to support C KVV spectrum decomposition which has therefore to rely upon a purely empirical basis. In addition, the introduction of disorder related effects is not straightforward for this spectrum. A real validation of the sp 2 fraction measurement is lacking for both techniques, though there are indications that both allow qualitative or even semi-quantitative (C 1s spectrum) understanding of the electronic structure of amorphous carbon systems. Beside the sp 2 fraction evaluation, other pieces of information, concerning the spatial organization of the sp 2 sites, are possibly extracted from these spectra.