The pioneering gas-liquid chromatographic studies in the early 1950s were carried out on packed columns in which the ststionary phase was a thin film of liquid retained by adsorption on the surface of a finely divided,inert solid support. From theoretical studies made during this early period, it became apparent that unpacked columns having inside diameters of a few tenths of a millimeter could provide separations that were superior to packed columns in both speed and column efficiency.In such capillary columns, the stationary phase was a film of liquid a few renths of a micrometer thick that uniformly coated the interior of a capillary tubing. In the late 1950s, such open tubular columns were constructed, and the prediched performance characteristic were experimentally confirmed in several laboratories, with open tubular columns having 300,000 plates or more being described.