Unfolded protein response is a complex cellular signaling pathway and a central academic concept in cell biology activated by the accumulation of misfolded or unfolded proteins, particularly within the endoplasmic reticulum. It represents a research field investigating the intricate mechanisms by which eukaryotic cells sense this proteotoxic stress and initiate adaptive transcriptional and translational programs aimed at restoring protein homeostasis (proteostasis) or, if stress is intractable, inducing apoptosis, underscoring its critical significance in cellular physiology and various disease states.