Abstract　 　 
Stars emit intense X-rays at almost every stage of formation and evolution. X-ray surveys of stars in several clusters show that young stars produce emission from similar processes as found in their main sequence counterparts: coronal emission from magnetically heated plasma in cool stars and shocks in radiatively driven winds in hot stars. Additional processes unique to young stars are also observed. In some cases the X-ray emission from the protostar itself can fluoresce the surrounding disk in Fe K alpha. The shock from the accelerating accretion flow onto classical T Tauri stars is observed through high resolution X-ray spectroscopy. Magnetic fields may be needed to explain the X-ray emission from young hot stars. Thus X-rays provide important new diagnostics of star-disk interaction. X-ray emission also affects the environments of young stars, and may be important for the production of planets.