This chapter discusses the energy at the surface either by conduction from within the volume interior to the surface or by convection or conduction at the surface from a surrounding medium. At each location along the surface, the radiation, convection, and conduction combine to form a thermal boundary condition. If the formulation includes axial conduction, there are two additional conduction boundary conditions. Numerical solution methods are presented and illustrated for radiation combined with conduction and/or convection. Heat conduction depends on the local temperature gradient. Convection depends approximately on the first power of the temperature difference. At moderate temperatures radiative fluxes are small, but in conjunction with natural convection in air that generally produces small convective heat transfer coefficients, the radiative transfer may be comparable to convection. For a fin on a surface, the net heat conduction along the fin is balanced by local radiative dissipation and natural convection.