The manipulation of electric charge in bulk semiconductors and their heterostructures is the basis of nearly all modern electronic and opto-electronic devices. Recent studies of spin-dependent phenomena in semiconductors open the door to technologies that harness the spin of the electron in semiconductor devices. In addition to providing spin-dependent analogies that extend existing electronic devices into the realm of semiconductor "spintronics," the spin degree of freedom also offers prospects for fundamentally new functionality in the quantum domain, ranging from storage to computation. This is likely to play a crucial role in the information technologies in the 21st century. This book, written by a team of experts, provides an overview of emerging concepts in this rapidly developing field. The topics range from spin transport and injection in semiconductors and their heterostructures to coherent processes and computation in semiconductor quantum structures and microcavities.