The end result of the antigen‐processing pathway is the display of peptide‐bound major histocompatibility complex I (pMHC I) molecules. The pMHC I molecules are expressed on the cell surface where they can be surveyed by CD8⁺ T cells for abnormal proteins. MHC I molecules present a large repertoire of peptides that fit perfectly in their binding grooves and represent the otherwise hidden intracellular contents. Many peptides originate as defective ribosomal products in the cytoplasm. In a stepwise manner, the antigen‐processing pathway generates and protects the proteolytic intermediates until they yield the final peptides that can fit the MHC I in the endoplasmic reticulum.