This book gives a comprehensive description of the physics and applications of resonant tunnelling diodes. The opening chapters of the book set out the basic principles of coherent tunnelling theory. The effects of impurity scattering, femtosecond dynamics, non-equilibrium distribution and intrinsic bistabilities are then described in detail. The applications of RTDs, such as in high-frequency signal generation and multi-valued data storage, are also reviewed. The book closes with a chapter devoted to the more recent field of resonant tunnelling through laterally confined zero-dimensional structures. Covering all the key theoretical and experimental aspects of this stimulating area of research, the book will be of great value to graduate students of quantum transport physics and device engineering, as well as to researchers in both these fields.