In the Fukushima Daiichi accident, the instrumentation provided for accident monitoring proved to be ineffective for a combination of reasons. The accident has therefore highlighted the need to re-examine criteria for accident monitoring instrumentation. This publication covers all relevant aspects of accident monitoring in nuclear power plants (NPPs). The critical issues discussed reflect the lessons learned from the Fukushima Daiichi accident, involve accident management and accident monitoring strategies for NPPs; 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.