  This review provides an introduction to non-geometric backgrounds in string
theory. Starting from a discussion of T-duality, geometric and non-geometric
torus-fibrations are reviewed, generalised geometry and its relation to
non-geometric backgrounds are explained and compactifications of string theory
with geometric and non-geometric fluxes are discussed. Furthermore covered are
doubled geometry as well as non-commutative and non-associative structures in
the context of non-geometric backgrounds.
