The physics of the Gruneisen parameter for solids is investigated from the view of conceptual and physical contributions. The relatively simple physics of a van der Waal's gas is applied to solid densities yielding a Gruneisen gamma approximately equal to 2. The separate electron and phonon contributions for metals are considered, and it is shown that except for very high and very low temperatures the phonon contribution dominates. Procedures for evaluating gamma from shock-Hugoniot data for isotropic solids are treated, and the necessity for applying ultrasonic data to anisotropic crystals is considered. The role of the more exotic thermal excitations of solid state physics in determining gamma is mentioned.