The status of optogalvanic (OG) spectroscopy, involving a change in the impedance of a gas or plasma, with tunable lasers is examined. The main advantage of this approach over the usual absorption spectroscopy is its high sensitivity. The OG effect in plasmas, glow discharges, hf discharges, hollow cathodes, obstructed discharges, neutral gases, etc., is studied. Optogalvanic studies of the spectra of both the ground and excited states of atoms and vibrational-rotational and electronic transitions in molecules, nonlinear spectroscopic phenomena, and interference of degenerate states and the use of the optogalvanic effect for stabilization of laser frequencies are described. A great deal of attention is given to the physical mechanisms involved in the formation of the OG signal. The possibilities for employing the optogalvanic effect in quantitative spectroscopy are evaluated.