Despite reliability improvements made to wind turbine drivetrains over the years, premature component failures are still challenging the wind industry. There are, however, opportunities to understand drivetrain reliability challenges and investigate potential mitigation solutions. This presentation discusses a few research and development (R&D) activities on drivetrain reliability carried out by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) over the last ten years. It covers two angles of reliability, inherent and operational, and goes into detail on specific R&D activities. Some inherent reliability challenges covered include gearbox planetary stage loads investigation, high speed shaft and main bearing operational condition understanding, dynamic modeling approaches, and recommended practices. The R&D activities on operational reliability improvements covered include benchmarking, performance and condition monitoring, and predictions on the remaining useful life of components. The presentation concludes with a list of necessary drivetrain reliability improvements that could close the loop between operational and inherent reliability efforts. The team hopes that some of these lessons learned can contribute to relevant international standards or recommended practices.