The initial step in infection of a cell by influenza A virus is the attachment of a virus particle to the target cell. This is accomplished by interaction of a glycoprotein, hemagglutinin (HA), found on the surface of the viral lipid membrane with cell-surface oligosaccharides containing sialic acids. All influenza virus attachment requires terminal sialic acid residues and two major linkages between sialic acid (Neu5Ac) and the penultimate galactose (Gal) residues of carbohydrate side chains are found in nature, Neu5Ac(α2,3)-Gal and Neu5Ac(α2,6)-Gal. The HA’s of different subtypes of influenza A virus exhibit different recognition specificities for these linkages and these linkage specificities have been correlated with host range specificity. The ability of the HA protein to differentiate sialic acid linkages makes it an interesting candidate for use in the characterization of glycoprotein's potentially facilitating the discrimination of alternate glycoforms of biopharmaceutical therapeutics and their subsequent purification.