Abstract The analytical benefits of comprehensive two-dimensional gas chromatography (GC × GC) methods have been exploited and emphasized in the past two decades. The unexpectedly complex nature of many real-world samples amenable to GC analysis has been elucidated through the enhanced resolving power of GC × GC. Simple but fundamental devices, called modulators, enable continuous heart-cutting and re-injection, without which GC × GC analysis cannot be achieved. The present review focuses on the history (1991–2010), and present trends and future prospects for GC × GC modulation. We provide detailed descriptions and set out the advantages and the disadvantages of the most significant thermal and pneumatic modulators.