This Photovoltaics Operations and Maintenance Best Practices Guide (PV O&M Guide) was initiated by the Solar Access to Public Capital (SAPC) Working Group, which issued an “interim” version in 2015 (http://www.nrel.gov/docs/fy15osti/63235.pdf). The SAPC Working Group was convened to open capital market investment in the solar asset class and consisted of solar developers, financiers and capital managers, law firms, rating agencies, accounting and engineering firms, and other stakeholders engaged in solar asset deployment. In 2016, a subset of the SAPC Working Group was merged with Sandia National Laboratories’ Technical O&M Working Group to unify efforts by the U.S. Department of Energy (DOE) to improve O&M practices, data standards, and costs. This combined body—the PV O&M Working Group—is administrated by the National Renewable Energy Laboratory (NREL), Sandia National Laboratories, SunSpec Alliance, and Roger Hill, and it is supported by the DOE SunShot Initiative (SuNLaMP program). One objective of the working group is to update, revise, and expand this guide, which was initially drafted as a compendium of O&M best practices to assist financiers in conducting due diligence on potential investments, as well as standardization of contracts, failure analysis, and support in developing standards.