Raman spectroscopy is a standard characterization technique for any carbon system. Here we review the Raman spectra of amorphous, nanostructured, diamond–like carbon and nanodiamond. We show how to use resonant Raman spectroscopy to determine structure and composition of carbon films with and without nitrogen. The measured spectra change with varying excitation energy. By visible and ultraviolet excitation measurements, the G peak dispersion can be derived and correlated with key parameters, such as density, sp3 content, elastic constants and chemical composition. We then discuss the assignment of the peaks at 1150 and 1480 cm−1 often observed in nanodiamond. We review the resonant Raman, isotope substitution and annealing experiments, which lead to the assignment of these peaks to trans–polyacetylene.