In the Fukushima Daiichi accident, the instrumentation provided for accident monitoring proved to be ineffective for a combination of reasons. The accident has highlighted the need to re-examine criteria for accident monitoring instrumentation. This publication covers all relevant aspects of accident monitoring in NPPs. The critical issues discussed reflect the lessons learned from the Fukushima Daiichi accident, involve accident management and accident monitoring strategies for nuclear power plants, selection of plant parameters for monitoring plant status, establishment of performance, design, qualification, display, and quality assurance criteria for designated accident monitoring instrumentation, and design and implementation considerations. Technology needs and techniques for accident monitoring instrumentation are also addressed.