Endoplasmic reticulum (ER) stress and oxidative stress are critical factors in cell fate decisions and human diseases. ER stress arises from protein misfolding and is regulated by the unfolded protein response (UPR), which includes pathways involving IRE1, PERK, and ATF6. These pathways help restore ER function but can also lead to apoptosis if stress is severe or prolonged. Oxidative stress, caused by reactive oxygen species (ROS), is generated in the ER and mitochondria during protein folding and mitochondrial respiration. ER stress and oxidative stress are closely linked, with each exacerbating the other in a positive feedback loop, leading to cellular dysfunction and apoptosis. The interplay between these stresses is crucial in various diseases, including metabolic, neurodegenerative, inflammatory, and neoplastic conditions. ER stress activates the UPR, which includes the IRE1-XBP1, PERK-eIF2α-ATF4-CHOP, and ATF6 pathways. These pathways regulate protein folding, ERAD, and autophagy, but their dysregulation can lead to oxidative stress and apoptosis. ROS production in the ER is linked to oxidative protein folding, and ER stress can increase mitochondrial ROS production, further contributing to oxidative stress. The UPR also influences oxidative stress through the activation of pro-apoptotic pathways and the regulation of antioxidant responses. In diseases such as diabetes, ER stress and oxidative stress are significant contributors to β-cell dysfunction and apoptosis. In metabolic diseases like non-alcoholic fatty liver disease (NAFLD), ER stress and oxidative stress are linked to hepatic dysfunction, lipid accumulation, and inflammation. In inflammatory diseases, ER stress and oxidative stress contribute to cellular dysfunction and inflammation, with the UPR playing a key role in inducing pro-inflammatory signals. In neoplastic diseases, ER stress and oxidative stress are involved in cancer progression, with the UPR helping cancer cells survive under stress conditions. Understanding the mechanisms of ER stress and oxidative stress is essential for developing novel therapeutic strategies for various human diseases. Targeting these pathways could provide new approaches for preventing and treating conditions associated with protein misfolding and oxidative stress.Endoplasmic reticulum (ER) stress and oxidative stress are critical factors in cell fate decisions and human diseases. ER stress arises from protein misfolding and is regulated by the unfolded protein response (UPR), which includes pathways involving IRE1, PERK, and ATF6. These pathways help restore ER function but can also lead to apoptosis if stress is severe or prolonged. Oxidative stress, caused by reactive oxygen species (ROS), is generated in the ER and mitochondria during protein folding and mitochondrial respiration. ER stress and oxidative stress are closely linked, with each exacerbating the other in a positive feedback loop, leading to cellular dysfunction and apoptosis. The interplay between these stresses is crucial in various diseases, including metabolic, neurodegenerative, inflammatory, and neoplastic conditions. ER stress activates the UPR, which includes the IRE1-XBP1, PERK-eIF2α-ATF4-CHOP, and ATF6 pathways. These pathways regulate protein folding, ERAD, and autophagy, but their dysregulation can lead to oxidative stress and apoptosis. ROS production in the ER is linked to oxidative protein folding, and ER stress can increase mitochondrial ROS production, further contributing to oxidative stress. The UPR also influences oxidative stress through the activation of pro-apoptotic pathways and the regulation of antioxidant responses. In diseases such as diabetes, ER stress and oxidative stress are significant contributors to β-cell dysfunction and apoptosis. In metabolic diseases like non-alcoholic fatty liver disease (NAFLD), ER stress and oxidative stress are linked to hepatic dysfunction, lipid accumulation, and inflammation. In inflammatory diseases, ER stress and oxidative stress contribute to cellular dysfunction and inflammation, with the UPR playing a key role in inducing pro-inflammatory signals. In neoplastic diseases, ER stress and oxidative stress are involved in cancer progression, with the UPR helping cancer cells survive under stress conditions. Understanding the mechanisms of ER stress and oxidative stress is essential for developing novel therapeutic strategies for various human diseases. Targeting these pathways could provide new approaches for preventing and treating conditions associated with protein misfolding and oxidative stress.