Formed between a H-bond acceptor and an H-bond donor. The simplest case is familiar: H2O, which is both an acceptor and a donor.

H-O ||| H-O
  |       |
  H       H
Where ||| represents the H-bond. Any polarisable hydrogen can be the donor for the bond, which may also be represented as donor|||H|||acceptor. This implies that the proton is shared by both molecules.

More unusual examples of H bonds include aromatic ring interactions, where a hydrogen bonds weakly to the face of the ring:

    |
    H
    _
    _
   __
  /  \
  \__/