Novel nontargeted analysis applications in two-dimensional gas chromatography–mass spectrometry (GC×GC–MS) and GC–high‑resolution (HR)MS have enabled the discovery of new contaminants. Now, the next frontier is nontargeted analysis for the elucidation of the mechanisms of (bio)chemical reactions in complex samples, such as the biodegradation of organics in water and soils or the conversion of plastics into oils. GC has the potential to contribute greatly to the optimization of these processes and therefore make a real contribution to net zero and circular economy agendas.