Supercritical pressure fluids have been exploited in many engineering fields, where binary mixtures are frequently encountered. This book focuses on the coupled heat and mass transfer in them, where the coupling comes from cross-diffusion effects (i.e., Soret and Dufour effects) and temperature-dependent boundary reactions. Under this configuration, three main topics are discussed: relaxation and diffusion problems, hydrodynamic stability, and convective heat and mass transfer. This book reports a series of new phenomena, novel mechanisms, and an innovative engineering design in hydrodynamics and transport phenomena of binary mixtures at supercritical pressures. This book covers not only current research progress but also basic knowledge and background. It is very friendly to readers new to this field, especially graduate students without a deep theoretical background.