  Research on graphene and other two-dimensional atomic crystals is intense and
likely to remain one of the hottest topics in condensed matter physics and
materials science for many years. Looking beyond this field, isolated atomic
planes can also be reassembled into designer heterostructures made layer by
layer in a precisely chosen sequence. The first - already remarkably complex -
such heterostructures (referred to as 'van der Waals') have recently been
fabricated and investigated revealing unusual properties and new phenomena.
Here we review this emerging research area and attempt to identify future
directions. With steady improvement in fabrication techniques, van der Waals
heterostructures promise a new gold rush, rather than a graphene aftershock.
