Many emerging applications of ionizing radiation require high-power linacs to provide the beam necessary for economical operation. This is particularly true when the electron beam is used for X-ray production. This presentation will review the status of both normal conducting and superconducting linacs as their development progresses towards supplying reliable beams of 100 kW or more. It will also be demonstrated that these new linacs will also require efficient, high-power RF sources in order to achieve full economic potential.