Continuous introduction of the sample feed, rather than a discrete injection pulse, defines frontal chromatography. As the feed enters the bed, the least-retained solute breaks through first as a sigmoidal front; more strongly retained solutes form later fronts, and the plateau concentrations and front positions report isotherms, binding capacities, and competitive adsorption ^[1]. In process chromatography the same frontal mode is used to pass a product while more strongly bound impurities (for example antibody aggregates) are retained, which is still frontal analysis rather than elution or displacement ^[2]. Conceptual boundaries exclude elution chromatography, in which a narrow feed band is developed by a weaker eluent, and displacement chromatography, in which a separate displacer forms an isotachic train. Essential features are uninterrupted feed, a stationary phase that is progressively saturated, and a breakthrough curve whose shape is governed by isotherm nonlinearity and axial dispersion ^[3]. Counter-current and membrane implementations retain the same frontal mass-balance structure while changing only the contacting geometry ^[4].