Widom (chemistry, Cornell U.) explains the chemistry uses of the theoretical apparatus used to study the properties systems made up of many atoms and molecules and relate those properties to microscopic constitutions. After explaining the derivation of common statistical thermodynamics formulas, chapters discuss applications such as the ideal gas, chemical equilibrium constants from partition functions, the ideal harmonic solid, and the statistical mechanical basis of the third law of thermodynamics. Also discussed are non-ideal and quantum ideal gases.