The final volume of James Clerk Maxwell's correspondence and manuscript papers covers the years 1874-1879, during Maxwell's Cambridge Professorship, his directing of the Cavendish Laboratory, and his work as writer and editor. His letters show his response to innovations in physical theory--by Boltzmann, Gibbs, Lorentz, and van der Waals--and further explorations in statistical physics and the kinetic theory of gases. His letters reflect his influence on the younger generation of physicists whose outlook was shaped by "Maxwellian physics". This edition is annotated with a full historical commentary.