Experimental Stanton number results are presented for the turbulent incompressible flat plate boundary layer with a variety of thermal boundary conditions—constant wall temperature, constant wall heat flux, and linear wall temperature variations. These experiments have extended the range of such heat transfer data to a Reynolds number, Rex, of 10 00 0000. The thermal boundary condition is found to have a significant influence on the behavior of the Stanton number. The experimental results are compared with the various heat transfer theories—analogies with skin friction, solutions of the integral boundary layer equations, and finite difference solutions of the Reynolds averaged boundary layer equations.