Although diazoalkanes are important carbene precursors in organic synthesis, a comprehensive mechanism of photochemical formation of carbenes from diazoalkanes has not been proposed. Synergies of experiments and computations demonstrate the involvement of higher excited singlet states in the photochemistry of diazoalkanes. In all investigated diazoalkanes, excitation to S-1 results in nonreactive internal conversion to S-0. On the contrary, excitation to higher-lying singlet states (S-n, n > 1) drives the reaction toward a different segment of the S-1/S-0 conical intersection seam and results in nitrogen elimination and formation of carbenes.