This safety research report examines the prevalence and risk factors of turbulence-related accidents in Title 14 Code of Federal Regulations Part 121 air carrier operations; assesses the effectiveness of policies, programs, technologies, and other applicable safety countermeasures; and makes recommendations for improving turbulence avoidance and injury mitigation. To conduct this research, the National Transportation Safety Board (NTSB) used both quantitative and qualitative methods, including a literature review, aggregate analysis of aviation accident data, and interviews with a broad selection of government, industry, and other stakeholders. In addition, the NTSB conducted 10 detailed investigations of turbulence-related Part 121 accidents over the course of this research. The NTSB identified the following safety issues: (1) insufficient submission and dissemination of turbulence observations, (2) a lack of shared awareness of turbulence risks, (3) the need for mitigation of common turbulence-related injury circumstances, and (4) the need for updated turbulence guidance. As a result of this safety research, the NTSB makes 18 new recommendations to the Federal Aviation Administration (FAA), 2 new recommendations to the National Weather Service, and 1 new recommendation to Airlines for America, the National Air Carrier Association, and the Regional Airline Association. The NTSB also reiterates three recommendations to the FAA and classifies and reiterates one additional recommendation to the FAA.