The ionization threshold energy of atoms and small molecules are typically larger than the photon energies that are most easily available experimentally. However, it can be possible to span this ionization threshold energy if the photon energy is resonant with an intermediate electronically excited state. While it is often possible to observe the lower Rydberg levels in conventional spectroscopy of atoms and small molecules, Rydberg states are even more important in laser ionization experiments. Laser spectroscopic experiments often involve ionization through a photon energy resonance at an intermediate level, with an unbound final electron state and an ionic core. On resonance for phototransitions permitted by selection rules, the intensity of the laser in combination with the excited state lifetime makes ionization an expected outcome. This RIS approach and variations permit sensitive detection of specific species.