Column temperatures well above ambient, typically from about 60 °C to more than 150 °C, define high-temperature liquid chromatography (HTLC) as a distinct operating regime of liquid chromatography. Elevated temperature lowers mobile-phase viscosity and increases solute diffusivity, which reduces back-pressure and can improve mass-transfer kinetics, while simultaneously shifting retention and sometimes selectivity ^[1]. Water and hydro-organic mixtures become less polar as temperature rises, so temperature can be used as a programmed variable analogous to solvent strength ^[2]. Conceptual boundaries exclude ordinary HPLC near room temperature, gas chromatography, and supercritical-fluid chromatography, although HTLC may approach the latter in solvent properties. Essential features are a thermally stable stationary phase, a preheater that brings the eluent to column temperature, and an analyte that remains chemically intact on the chromatographic timescale ^[3]. Practice and theory of the technique treat temperature as a thermodynamic and kinetic parameter of the same adsorption or partition equilibria that operate at ambient temperature, not as a separate separation mechanism ^[4].