Ureas and thioureas are frequently employed in the construction of supramolecular host systems, to which they can impart strong hydrogen bonding capabilities . Syntheses based on urea and thiourea linkages provide access to further chemical diversity, because isothiocyanates and isocyanates are available with a variety of substituents. Here, the nucleophilic addition of such reactants affords a range of urea and thiourea derivatized β-CD analogues, exemplified by 17-20 (Figure ). These syntheses also offer insight into the determinants of reactivity, as follows.