Remarkable advances in semiconductor growth and processing technologies continue to have a profound impact on condensed-matter physics and to stimulate the invention of novel optoelectronic effects. Intensive research on the behaviours of free carriers has been carried out in the two-dimensional systems of semiconductor heterostructures and in the one and zero-dimensional systems of nanostructures created by the state-of-the-art fabrication methods. These studies have uncovered unexpected quantum mechanical correlations that arise because of the combined effects of strong electron-electron interactions and wave function confinement associated with reduced dimensionality. The investigations of these phenomena are currently at the frontiers of condensed-matter physics. They include areas like the fractional quantum Hall effect, the dynamics of electrons on an ultra short (femtosecond) time scale, electron behaviour in quantum wires and dots, and studies of electron tunneling phenomena in ultra-small semiconductor structures. Optical techniques have made important contributions to these fields in recent years. The book provides an overview of these recent developments that should be of interest to semiconductor materials scientists in university, government and industrial laboratories.