Accumulation of misfolded proteins in the endoplasmic reticulum triggers a cellular stress response called the unfolded protein response (UPR) that protects the cell against the toxic buildup of misfolded proteins. Neurodegenerative disorders like Alzheimer’s disease, Parkinson’s disease, prion disease, Huntington’s disease, frontotemporal dementia, and amyotrophic lateral sclerosis are characterized by the accumulation and aggregation of misfolded proteins. In this chapter we will discuss the different levels of protein quality control systems in the endoplasmic reticulum. The role of these systems and especially the UPR will be reviewed in view of current data about the expression and role of the UPR markers in the pathology of neurodegenerative disorders.