The Physibel software is a set of programs for heat transfer simulation, focussing on building physics. The software is based on physical models of heat transfer by conduction, radiation and convection, in 1D, 2D and 3D, both steady state and transient. Application domains are rational use of energy in buildings, thermal comfort in buildings, thermal analysis of building components and of whole buildings, optimizing building thermal quality by avoiding moisture problems. During the seminar the software is demonstrated and results of relevant applications are shown.