The challenge of achieving maximal dopant activation with minimal diffusion has re-awakened interest in millisecond-duration annealing processes, almost two decades after the initial research in this field. Millisecond annealing with pulsed flash-lamps or scanned energy beams can create very shallow and abrupt junctions with high concentrations of electrically active carriers, but solutions for volume manufacturing must also meet formidable process control requirements and economic metrics. The repeatability and uniformity of the temperature cycle is the key for viable manufacturing technology, and the lessons from the development of commercial rapid thermal processing (RTP) tools are especially relevant. Advances in the process capability require a fuller understanding of the trade-off between dopant activation, defect annealing. diffusion and deactivation phenomena. There is a strong need for a significant expansion of materials science research into the fundamental physical processes that occur at the short time scales and high temperatures provided by millisecond annealing.