Yeast surface display system had been developed greatly since the phage display was invented. It is well suitable for displaying mammalian cell-surface and secreted proteins that require endoplasmic reticulum-specific post translational processing for efficient folding and activity. Yeast cells are large enough particles, unlike phage, that can be screened and separated using flow cytometer. Yeast adhesion receptor, a agglutinin or α agglutinin, have been used as a surface display scaffold. Yeast surface display has been successfully applied in protein directed evolution and alive oral vaccines.