The self-consistent phonon theory of anharmonic lattice dynamics, devised independently by several authors using varying techniques and implemented computationally by Koehler, is here applied to the crystals of neon and argon. A Lennard-Jones 6-12 interatomic potential is assumed. The quantities calculated are the phonon spectrum and the bulk thermodynamic properties of thermal expansion, compressibility, and specific heat, all as a function of temperature at zero pressure. Although the computations are intended primarily to explore in detail the content of the self-consistent phonon approximation preparatory to incorporating the more elaborate expressions of the next higher approximation, comparison is made with the existing experimental data. © 1968 The American Physical Society.