Online monitoring (OLM) technologies have been developed and validated for a variety of applications in nuclear power plants including optimizing maintenance of instrumentation and controls (I&C) systems, detection of process anomalies such as blockages, leaks, voids, flow anomalies, excessive vibration, overheating, and equipment or process deviations from normal behavior. For example, the Sizewell B nuclear power plant (NPP), a Westinghouse pressurized water reactor (PWR) in the United Kingdom (U.K.), implemented OLM for transmitter calibration verification and has been using it effectively for over a decade. With the help of OLM technologies, today Sizewell B is calibrating only those transmitters that are found by OLM to drift beyond acceptable limits plus one transmitter from each redundant set to account for any systematic drift. Since the late 1990’s, several industry organizations, academic institutions, national laboratories, vendors, and others have worked on the application of OLM technologies to extend transmitter calibration intervals in NPPs in the U.S. In fact, in 2000, the U.S. Nuclear Regulatory Commission (NRC) issued a Safety Evaluation Report (SER) authorizing the use of OLM for transmitter calibration extensions subject to 14 stipulations. However, since that time, no U.S. utility has implemented OLM for transmitter calibration interval extension presumably because the industry found a few of the NRC’s stipulations in the SER to be too restrictive and cost prohibitive to resolve. Today, it has been over 18 years from when the NRC issued the SER and much has happened since then including: 1) successful OLM implementation at Sizewell B with approval of U.K. regulators, 2) OLM implementation at over ten U.S. PWRs on a demonstration basis, 3) continued research by the nuclear industry and academia to address essentially all technical questions and regulatory concerns, 4) Probabilistic Risk Assessment (PRA) work showing the very low risk of extending transmitter calibration intervals, and 5) additional operating experiences (OEs) demonstrating that the current generation of nuclear grade pressure, level, and flow transmitters do not normally drift enough to need a calibration at each refueling outage. These developments have provided sufficient evidence to propel OLM for ready implementation in nuclear power plants and have provided answers to many of the 14 NRC stipulations in the SER. As such, OLM is ready for implementation in U.S. nuclear power plants provided that the NRC can be convinced of its validity, reliability, and safety. This paper provides details of a project conducted by the authors under the auspices of the U.S. Department of Energy (DOE) to work with the NRC to document the technical foundation and address the regulatory issues for implementation of OLM to extend the calibration intervals of pressure, level, and flow transmitters in NPPs. The product of this project will be a report to be used by the nuclear industry for guidance on OLM implementation that can satisfy the NRC. As importantly, the product of this work will provide the NRC with the information and data that it needs to review plant applications for OLM implementations.