The article reviews the progress and challenges in FLASH radiotherapy (FLASH RT), a promising approach that uses ultra-high dose rates (UHDRs) to reduce normal tissue damage while maintaining tumor control. Preclinical studies and initial clinical trials have shown that FLASH RT can significantly reduce normal tissue injury, particularly in the lung, brain, skin, intestine, and blood. However, the biological mechanisms behind the FLASH effect remain largely unknown, and further research is needed to fully understand the radiobiological mechanisms and optimize treatment parameters. The article highlights the importance of in vitro studies to investigate DNA damage and other cellular responses to UHDR irradiation. Additionally, technological advancements in beam generation, such as laser-driven plasma accelerators, are crucial for developing compact and affordable clinical accelerators capable of delivering FLASH RT. Despite the progress, significant challenges remain, including the need for more comprehensive clinical trials and the development of advanced treatment planning systems. The authors emphasize the importance of continued research to fully realize the potential of FLASH RT in radiation oncology.The article reviews the progress and challenges in FLASH radiotherapy (FLASH RT), a promising approach that uses ultra-high dose rates (UHDRs) to reduce normal tissue damage while maintaining tumor control. Preclinical studies and initial clinical trials have shown that FLASH RT can significantly reduce normal tissue injury, particularly in the lung, brain, skin, intestine, and blood. However, the biological mechanisms behind the FLASH effect remain largely unknown, and further research is needed to fully understand the radiobiological mechanisms and optimize treatment parameters. The article highlights the importance of in vitro studies to investigate DNA damage and other cellular responses to UHDR irradiation. Additionally, technological advancements in beam generation, such as laser-driven plasma accelerators, are crucial for developing compact and affordable clinical accelerators capable of delivering FLASH RT. Despite the progress, significant challenges remain, including the need for more comprehensive clinical trials and the development of advanced treatment planning systems. The authors emphasize the importance of continued research to fully realize the potential of FLASH RT in radiation oncology.