Nearly ten million people die from cancer each year, making it one of the top causes of mortality worldwide in 2024. Delivering ultra-high-dose radiation in a split second makes FLASH radiotherapy a novel method in cancer treatment. This method departs greatly from traditional radiotherapy by making use of the distinct biological reactions that high-dose radiation, given quickly, can trigger. Electron FLASH therapy, proton FLASH therapy, and photon FLASH therapy utilize electron beams, photon beams, proton beams, and heavy-ion beams, employing linear electron accelerators (LINACs) to deliver radiation at rates exceeding 40 Gy/s. These therapies are effective in targeting cancerous cells with high specificity and reduced cytotoxicity to healthy cells.. FLASH therapy has demonstrated promise in reducing radiation-induced toxicity and enhancing tumor control compared to conventional methods. Recent research indicates that FLASH radiation therapy improves the overall therapeutic window and minimizes acute adverse effects. Mechanistically, the rapid delivery of radiation appears to activate different cellular and molecular pathways, including those involved in DNA damage repair, immune modulation, and oxidative stress responses. Preclinical models have demonstrated promising results, indicating that FLASH radiotherapy can be effective across various tumor types, including those resistant to traditional radiation therapies. Moreover, advancements in accelerator technology are facilitating the application of FLASH radiation in clinical settings, paving the way for professional trials that will further elucidate its efficacy and safety profile.