The BiP protein, also known as Binding immunoglobulin protein or HSPA5, is a crucial molecular chaperone located in the endoplasmic reticulum (ER) that belongs to the Hsp70 family. BiP binds to hydrophobic amino acid residues of unfolded proteins entering the ER, preventing incorrect folding and aggregation. It also interacts with folded proteins to protect them from aggregation and degradation. Under ER stress conditions, BiP interacts with ER stress sensors such as ATF6, IRE1α, and PERK, regulating their activation and initiating the ER stress response pathway to help cells cope with unfolded protein accumulation. Due to its essential role in the cell, abnormal expression or dysfunction of BiP is closely related to the development of various diseases. For instance, BiP is overexpressed in tumor cells, associated with tumor invasion, metastasis, and drug resistance. Additionally, some genetic and neurodegenerative diseases are linked to abnormal expression or dysfunction of BiP.