A topic of great present interest is the investigation of heat transfer in materials with memory (HTMM). The correct description of different experimental heat transfer phenomena (in liquid helium, in dielectrics at helium temperature, in organic liquids, etc.) is conducted on the framework of HTMM theory. Also, new physical effects have been predicted in HTMM theory. The most important problem for HTMM theory and practical applications is analyzed—the propagation of harmonic thermal waves in an infinite plate from material with thermal memory. It is shown that in such materials there are appreciable effects produced by the interference of thermal waves, similar to multibeam interference of electromagnetic waves in optics. ©1997 American Institute of Physics.