The advent of highly sensitive ionization detectors in recent years has made gas chromatography one of the most useful analytical tools available to the organic chemist. One extremely effective technique of sample ionization not yet adapted for practical use in this field is that of photoionization. A comprehensive study has been made of a photoionization detector for gas chromatography systems. Initial characterization of detector geometry and operating parameters was accomplished using a flexible breadboard apparatus. Three optimized detector designs which resulted were subjected to comparative evaluations. The best performing of these devices was selected for detailed characterization. Performance of this detector compared favorably with the best of the ionization detectors currently employed in gas chromatography. Sample response was almost three orders of magnitude greater and noise level only an order of magnitude higher than those of commercial flame ionization detectors. Detector stability was good. Best performance was achieved by operating at reduced pressures using a DC discharge in argon and employing hydrogen as the carrier gas. The use of helium and other sources of high energy photons as discharge gases appeared considerably complicated by even trace amounts of impurities. Detector response to numerous organic and inorganic compounds was determined. Successful applications were made in the fields of air pollution analyses and in the analysis of hydrocarbons extracted from meteorites. Space probe applications were also examined. The extreme sensitivity and potential selectivity of this detector recommend it highly for use in chromatographic systems.