Narrow-bore open or packed capillaries, rather than conventional wide-bore packed columns, constitute the geometric defining feature of capillary chromatography. The small inner diameter reduces plate height and solvent consumption and permits electrokinetic as well as pressure-driven flow. Micellar electrokinetic capillary chromatography (MEKC) superimposes a charged micellar pseudostationary phase on capillary electrophoresis, so that neutral and charged solutes acquire differential migration through chromatographic partition into the micelles in addition to electrophoretic mobility ^[1]. Packed or monolithic capillaries with immobilized ligands, including aptamers, provide a true stationary phase inside the same capillary format ^[2]. Conceptual boundaries exclude ordinary packed-column HPLC of several millimetres internal diameter, and they exclude free-zone capillary electrophoresis that lacks a chromatographic partition medium. Essential features are a capillary conduit, a defined stationary or pseudostationary phase, and a driving force—pressure, electroosmosis, or both—that transports the mobile phase ^[3]. Two-dimensional couplings of capillary sieving electrophoresis with MEKC further illustrate that the capillary is the format, while the retention chemistry may vary ^[4].