  We review the basic physics of repulsively bound atom pairs in an optical
lattice, which were recently observed in the laboratory, including the theory
and the experimental implementation. We also briefly discuss related many-body
numerical simulations, in which time-dependent Density Matrix Renormalisation
Group (DMRG) methods are used to model the many-body physics of a collection of
interacting pairs, and give a comparison of the single-particle quasimomentum
distribution measured in the experiment and results from these simulations. We
then give a short discussion of how these repulsively bound pairs relate to
bound states in some other physical systems.
