Energy levels, specific mass shift parameters, hyperfine interaction constants, Landé g J factors, and tran-sition probabilities between computed levels are reported for C II, N III, and O IV. Results include levels belonging to 2s 2 2p;2s2p 2 ; 2p 3 ; 2s 2 3s;2s 2 3p;2s 2 3d;2s2p3s and, in the case of C II, the 2s 2 4s and 2s 2 4p con-figurations. Wavefunctions were determined using the multiconfiguration Dirac–Hartree–Fock method and account for valence, core–valence, and core–core correlation effects.