Recent advances in the understanding of the factors which determine line intensities in zero kinetic energy photoelectron spectroscopy (ZEKE-PES) are reviewed. The relative importance of direct ionization and autoionization is assessed. Explicit consideration of the channel interactions which take place in the vicinity of molecular ionization thresholds leads to a general discussion of rotational line intensities in ZEKE-PES. A series of limiting cases is proposed to assist in the interpretation of experimental results. Finally a new dynamical interpretation of ZEKE experiments based on the trapping of the ZEKE electrons in non-penetrating high-lRydberg orbitals by weak electric fields appears to give a satisfactory explanation of most experimental results obtained to date.