A more strongly retained displacer that advances as a sharp front and competitively desorbs weaker solutes defines displacement chromatography. After the feed is loaded, a displacer solution is introduced; solutes leave the column as adjacent, high-concentration isotachic bands ordered by binding affinity, rather than as diluted Gaussian peaks produced by an eluent that is weaker than the solutes ^[1]. On synthetic ion-exchange resins, amino acids form ordered displacement zones according to competitive binding strength; this differs from frontal analysis, in which the sample itself is the only feed ^[2]. Cation-exchange displacement of differently charged proteins confirms that the defining element is the displacer-driven band train rather than a particular adsorbent chemistry ^[3]. Essential features are a displacer whose affinity exceeds that of all targets, a loading high enough to enter the nonlinear isotherm region, and a regeneration step that removes the displacer. Conceptual boundaries exclude gradient elution, in which solvent strength, not a displacer front, releases the solutes ^[4].