  Over the last decades, numerous wide (>1000 AU) binaries have been discovered
in the Galactic field and halo. The origin of these wide binaries cannot be
explained by star formation or by dynamical interactions in the Galactic field.
We explain their existence by wide binary formation during the dissolution
phase of young star clusters. In this scenario, two single stars that leave the
dissolving cluster at the same time, in the same direction, and with similar
velocities, form a new, very wide binary. Using N-body simulations we study how
frequently this occurs, and how the orbital parameters of such binaries depend
on the properties of the cluster from which they originate. The resulting wide
binary fraction for individual star clusters is 1-30%, depending on the initial
conditions. As most stars form as part of a binary or multiple system, we
predict that a large fraction of these wide binaries are in fact wide triple
and quadruple systems.
