The recent rise of vancomycin-resistant enterococci (VRE) and vancomycin-resistant Staphylococcus aureus (VRSA) has given new impetus to the study of the binding between glycopeptide antibiotics and bacterial cell wall termini. Here, we report on an extensive first principles investigation of the binding of vancomycin, avoparcin, teicoplanin, and ristocetin aglycons with dipetides, Ac-D-Ala-X, where X = D-Lac and D-Ser (characteristic of VREs) and X = D-Ala, Gly (characteristic of non-VREs), and a model "methylated D-Ala" CH2CH(CH3)COO-, in liquid as well as gas phase. The gas-phase ordering of the binding, from strongest to weakest, is Gly, D-Ala, D-Ser, CH2CH(CH3)COO-, and D-Lac. Calculations show that the order of the Gly and D-Ala binding is reversed in solution. The results are in good agreement with recent experimental findings.