Size-exclusion separation in a porous gel, rather than adsorption or ion exchange, defines gel permeation chromatography (GPC) as used for macromolecules and many natural-product polymers. Solutes that are too large to enter the pores travel with the interstitial solvent and elute first; smaller solutes permeate a larger fraction of the internal pore volume and are retained longer, so that elution volume maps onto hydrodynamic size ^[1]. The stationary phase is typically a cross-linked polymer or silica gel whose pore-size distribution is matched to the analyte range, and the mobile phase is chosen to suppress adsorptive interactions that would overlay a secondary retention mechanism ^[2]. Multidetection GPC combines the size separation with light scattering, viscometry, or concentration detectors to convert the elution profile into a molecular-weight distribution ^[3]. Conceptual boundaries exclude adsorption chromatography, ion-exchange chromatography, and filtration that lacks a defined chromatographic plate structure. Essential features are an inert porous network, a calibration or absolute-detector relation between elution volume and size, and a mobile phase that preserves the exclusion mechanism.