The gas chromatography/mass spectrometry (GC/MS) interface is the section of the instrument starting at the column exit in the gas chromatograph and extending to the entrance to the ion source of the mass spectrometer. For most applications of modern GC/MS instrumentation, the GC/MS interface is a heated metal tube equipped with a temperature controller. This chapter illustrates the open-split interface that offers a convenient connection between the GC column and the mass spectrometer. The open-split interface gives the better chromatographic integrity of the two types of interfaces. The chromatographic integrity is even better than that which can be obtained with the direct introduction of the column into the ion source. The open-split interface has been found to discriminate against higher-mass and higher-boiling compounds, a feature that will limit its usability. The most popular of the various enrichment devices used with packed columns was the jet-orifice separator invented. It continues to be used in modern instrumentation with capillary columns. The jet separators are prone not only to occasional clogging most often with condensed stationary phase that has bled out from the column but also with deposits of organic material that can condense on the orifice. One important disadvantage to the jet separator is that it must have a flow rate of ∼20 mL per minute to perform properly. With this added complication for the use of the jet separator, the results obtained in terms of detection limits are not that much better than those that can be achieved with the open-split interface.