We review the literature on comprehensive two-dimensional gas chromatography (GC × GC), emphasizing developments in the period 2003-2005. The review opens with a general introduction, the principles of the technique and the set-up of GC × GC systems. It also discusses theoretical aspects, trends in instrumentation, column combinations, and detection techniques - notably mass spectrometric detection. We devote attention to a wide variety of applications and to analytical performance. Part II discusses the key aspects of modulation and the various modes of detection. © 2006 Elsevier Ltd. All rights reserved.