  Besides the familiar D-branes, string theory contains a vast number of other
non-perturbative objects. While a complete classification is lacking, many of
these objects are related to each other through various dualities. Codimension
two objects play a special role, because their charges are no longer additive
but are instead expressed in terms of holonomies of scalar fields, which is
given by an element of the relevant duality group. In this paper we present a
detailed exposition of these "exotic" objects, the charges they carry, and
their connection to non-geometric compactifications. Despite the name "exotic
branes," these objects are in fact ubiquitous in string theory, as they can
automatically appear when describing bound states of conventional branes, and
as such may be of particular importance in describing the microscopic degrees
of freedom of black holes.
