Thermal effects in aircraft may arise from kinetic heating, engine installations and auxiliary systems. The first source is potentially of greater importance, although problems in connection with the second source can be severe, especially with vertical take-off aircraft of the “flying bedstead” type. The difficulty encountered in a formal analysis of heat conduction problems when practical boundary conditions are to be satisfied frequently suggests a finite difference approach. This may take the form of direct numerical integration or the use of digital or analogue computers or network analysers in which electrical circuits are arranged to be analogous to the thermal system. Several examples illustrating the use of these finite difference methods are instanced, such as the growth of temperature in a thick plate, the transient distribution of temperature in a rib carrying a hot duct; the chordwise distribution of temperature and transient loss in torsional stiffness in a thin wing due to kinetic heating, and the distribution of temperature and spanwise thermal stress due to kinetic heating in a bay of an integrally stiffened panel. The importance of experimental methods is emphasised and a brief description and illustration of a model fuel tank for simulated kinetic heating tests is given. An urgent plea is made for correlated data on thermal contact resistance of typical aircraft joints, some examples of which are also illustrated. Data is given on some physical and mechanical properties of materials likely to be used for airframes where thermal effects are expected. These include thermal expansion, conductivity, diffusivity, creep, fatigue, specific strength and stiffness, and a parameter called here the “Thermal Stress Efficiency.”