One of the most commonly encountered non-covalent interactions is the hydrogen bond (HB; Fig. . Ubiquitous in nature, the relatively weak nature of HBs (typically <40 kJ mol -1 although estimates vary 139 ) is both a gift and a curse. The low energy barrier to rearrangement allows funnelling of selfassembled mixtures down to their thermodynamic minimum with relative ease. The susceptibility of the HB to unwanted disruption, however, limits the stability of such systems, and makes their design a significant challenge. The simplest form of HB capsules would therefore arise from homomeric dimerization of self-complementary building blocks (Fig. ). In 1993, Rebek and co-workers introduced curved glycouril-based monomer 70 that was shown to self-assemble into a dimeric capsule in chloroform, forming a molecular tennis-ball held together by a seam of 8 HBs between the glcouril units. Encapsulation of small molecule guests (chloroform, dichloromethane, methane, ethylene) was demonstrated by NMR, with slow exchange evidenced by observed signals for both the empty capsule and host-guest adduct. Since this seminal work, other examples of hydrogenbonded dimers have been reported from interactions between various functional groups (Fig. ), such as peptides, 142 oximes, 143 amides, 144 ureas (e.g. 71), and resorcinarenes (e.g. 72, 73). For each of these, self-assembly in chloroform proceeded readily, whilst addition of competing solvents (methanol, DMSO) served to disrupt the HB interactions between monomers.