This book deals with optical properties of semiconductors at extremely short (pico- and femtosecond) time scales. The contributions, by an international roster of researchers, cover current research on a wide array of topics. Topics covered include: 1. Coherent Dynamics of Photoexcited Semiconductor Superlattices with Applied Homogeneous Electric Fields (Koch,Meier,Thomas) 2. Ultrafast non-equilibrium dynamics of intersubband excitations in quasi two dimensional semiconductors (Elsaesser,Woerner MPI Berlin) 3. Bloch-Oscillations in Semiconductors: Principles and Applications (Leo, TU Dresden) 4. Electron-velocity overshoot, electron ballistic transport and nonequilibrium phonon dynamics in nanostructure semiconductors (Tsen, Arizona State) 5. Coherent Control of Photocurrents in Semiconductors (Van Driel,Sipe U Toronto ) 6. Ensemble Monte Carlo Simulations of Ultrafast Phenomena in Semiconductors (Ferry & Goodnick, Arizona State) 7. Theory of Coherent Phonon Oscillations in Bulk GaAs (Stanton & Kuznetsov, U Florida) 8.Coherent Spectroscopy on Quantum Wires (Forchel, Bayer, & Bacher, U Wuerzburg) 9. The Vectorial Dynamics of Coherent Emission from Excitions (Smirl, U Iowa)