The chapter begins by showing the fundamental differences between the disciplines of Heat Transfer and Thermodynamics with the aid of ordinary examples, which will help the students to perceive those differences. The chapter briefly presents the three modes of heat transfer, which are conduction, convection, and thermal radiation, in addition to the diffusive and convective modes of mass transfer. The physical principles governing heat conduction, Fourier's law of conduction, and the definition of thermal conductivity, k, are presented. Newton's law of convection is introduced, when the heat transfer coefficient, h, is defined. The third form of heat transfer by thermal radiation is presented next, with the definition of the Stefan-Boltzmann law. Finally, diffusive mass transfer, given by Fick's law, and convective mass transfer are presented. The diffusion coefficients, \(D_{AB}\) , and convection of mass, km, are defined. Several solved exercises are presented, and at the end, proposed problems are presented.