The invention includes glycopeptides having a glycoside and a peptide covalently bound through an amide bond. The glycopeptides may also include a diagnostic or therapeutic agent bound to the glycopeptide. A metal, such as a radionuclide, may also be chelated to the glycopeptide. Specific embodiments of the invention relate to glycopeptides made of chitosan covalently bound to a poly(amino acid) such as poly(glutamic acid) or poly(aspartic acid). Diagnostic agents conjugated to the glycopeptide may facilitate imaging. Specific therapeutic agents that may be conjugated to the glycopeptide include anticancer drugs, rheumatoid arthritis drugs, anticoagulants, anti-angiogenesis drugs, apoptosis drugs, osteoporosis drugs, steroids, and anti-inflammatory drugs. Some agents, such as radionuclides, may have both diagnostic and therapeutic effects. The glycopeptides may be made by combining a glycoside and a peptide in the presence of a carbodiimide and an acid group activator to form an amide bond between the glycoside and the peptide.