Book excerpt: Foreword by Charles H Townes This volume includes highlights of the theories underlying the essential phenomena occurring in novel semiconductor lasers as well as the principles of operation of selected heterostructure lasers. To understand scattering processes in heterostructure lasers and related optoelectronic devices, it is essential to consider the role of dimensional confinement of charge carriers as well as acoustical and optical phonons in quantum structures. Indeed, it is important to consider the confinement of both phonons and carriers in the design and modeling of novel semiconductor lasers such as the tunnel injection laser, quantum well intersubband lasers, and quantum dot lasers. The full exploitation of dimensional confinement leads to the exciting new capability of scattering time engineering in novel semiconductor lasers.As a result of continuing advances in techniques for growing quantum heterostructures, recent developments are likely to be followed in coming years by many more advances in semiconductor lasers and optoelectronics. As our understanding of these devices and the ability to fabricate them grow, so does our need for more sophisticated theories and simulation methods bridging the gap between quantum and classical transport.