Two apparently disparate lines of inquiry in kinetic theory are shown to be equivalent: (1) Brownian motion as treated by the (stochastic) Langevin equation and Fokker‐Planck equation; and (2) Boltzmann's equation. The method is to derive the kinetic equation for Brownian motionfromthe Boltzmann equation for a two‐component neutral gas by a simultaneous expansion in the density and mass ratios.