Glycans or carbohydrates that cover the surface of all living cells have developed into a kind of species-specific molecular passport that help determine how our organisms recognize invading pathogens, cancer cells or recognize proteins and cells of the same organism. The weak but specific forces between single carbohydrates and proteins are reinforced through various levels of polyvalent presentation on the protein or cell level leading to interactions of high strength and specificity which can even outperform antibody-antigen binding. We will look at the role of glycans in cell-pathogen communication, assess their opportunities as functional biomarkers and fantasize on the potential of multivalent glycomimetics in immune therapy.