ATM and ATR are crucial cell cycle checkpoint kinases responsible for sensing DNA damage and initiating the cellular repair processes. ATM primarily responds to double-strand breaks, while ATR is more sensitive to single-strand DNA damage. Both belong to the PIKK family, consisting of a kinase domain and a series of regions for protein interactions. They localize within the cell nucleus and, through phosphorylation of downstream effector molecules such as p53 and CHK1/CHK2, activate DNA repair pathways and induce cell cycle arrest. The gene expression of ATM and ATR is highly tissue-specific, and their dysfunction or mutations are closely associated with the development of various genetic disorders and cancers.