Stable isotope probing is a molecular technique that employs substrates enriched with stable isotopes to trace their metabolic incorporation into biomolecules, thereby identifying and characterizing the activity of organisms or processes within a complex system. This method is significant for linking metabolic function to taxonomic identity or specific biochemical pathways without the need for cultivation, providing insights into nutrient cycling, trophic interactions, and the functional roles of organisms in diverse environments by subsequent analysis of the labeled material using techniques like mass spectrometry or density gradient centrifugation.