The endoplasmic reticulum (ER) is a complex network of membranes within cells that plays a crucial role in protein synthesis, folding, and transport. When cells experience stress, such as nutrient deprivation, oxidative stress, or changes in calcium levels, the ER can become overwhelmed and protein folding may become impaired. This leads to the accumulation of misfolded proteins in the ER, a condition known as ER stress. ER stress triggers a cellular response known as the unfolded protein response (UPR), which aims to restore ER homeostasis by increasing the production of chaperone proteins that help with protein folding, reducing protein synthesis, and activating pathways that promote cell survival or trigger cell death in severe cases. Research on ER stress and the UPR is important for understanding and treating various diseases, including neurodegenerative disorders, metabolic diseases, and cancers, which are often associated with ER stress. By studying the mechanisms underlying ER stress and the UPR, researchers are working to develop new therapeutic approaches that target these pathways to alleviate ER stress-induced cell damage and dysfunction.