The results of numerical computations are presented for free convection under isothermal wall and constant-heat-flux wall-boundary conditions. The effects of the Prandtl, Grashof, and Rayleigh numbers, aspect ratio, and variable properties are described. Experimental measurements of net heat transfer through vertical plane layers and of velocity and temperature profiles are given for Prandtl numbers of 1 to 20,000. A comparison of the laminar data with the numerical results shows excellent correlation.