Gas chromatography (GC) is one of the most important techniques of organic analytical chemistry. It is widely used in the analysis of complex samples in environmental and medical applications. In order to reliably identify and quantitate the analyte that often exists at a residual concentration level, the GC system must in many cases have a separation power that cannot be achieved using one column within a reasonable analysis time. An extremely high resolution can be achieved by two-stage GC (multidimensional GC, two-dimensional GC), where the sample flows of two GC columns have been connected on-line by a valve or valve system in such a way that only a selected fraction from the partly separated sample eluting from the first column can be transferred to the second column for further separation. This review describes the development of the technique and discusses areas of its applicability.