The invention relates to cellular localization signals. In particular, the invention relates to endoplasmic reticulum localization signals in monomeric or multimeric form. The localization signals are utilized as research tools or are linked to therapeutics. Disclosed are methods of making and using polypeptides and modified polypeptides as signals to localize therapeutics, experimental compounds, peptides, proteins and/or other macromolecules to the endoplasmic reticulum of eukaryotic cells. The polypeptides of the invention optionally include linkage to reporters, epitopes and/or other experimental or therapeutic molecules. The invention also encompasses polynucleotides encoding the localization signals and vectors comprising these polynucleotides.