  This is a review of exceptional field theory: a generalisation of
Kaluza-Klein theory that unifies the metric and $p$-form gauge field degrees of
freedom of supergravity into a generalised or extended geometry, whose
additional coordinates may be viewed as conjugate to brane winding modes. This
unifies the maximal supergravities, treating their previously-hidden
exceptional Lie symmetries as a fundamental geometric symmetry. Duality orbits
of solutions simplify into single objects, that in many cases have simple
geometric interpretations, for instance as wave or monopole-type solutions. It
also provides a route to explore exotic or non-geometric aspects of M-theory,
such as exotic branes, U-folds, and more novel sorts of non-Riemannian spaces.
