IRE1 (Inositol-Requiring Enzyme 1) is a key component of the endoplasmic reticulum stress response, consisting of two subtypes, IRE1α and IRE1β. It features a transmembrane domain spanning the endoplasmic reticulum membrane, an endoplasmic reticulum lumen-sensing domain, and a cytoplasmic RNase and kinase activity domain. IRE1 localizes on the endoplasmic reticulum membrane, responding to protein folding disturbances. Through its RNase activity, it cleaves XBP1 mRNA, activating the expression of anti-stress genes. Through its kinase activity, it participates in various signaling pathways such as JNK activation. The expression and activity of IRE1 regulate cellular adaptation to endoplasmic reticulum stress. Gene-specific expression and mutations are associated with various diseases including inflammation, tumors, and metabolic disorders. IRE1 plays a crucial role in cellular survival and death decisions.