  Dawn-dusk asymmetries are ubiquitous features of the coupled
solar-wind-magnetosphere-ionosphere system. During the last decades, increasing
availability of satellite and ground-based measurements has made it possible to
study these phenomena in more detail. Numerous publications have documented the
existence of persistent asymmetries in processes, properties and topology of
plasma structures in various regions of geospace. In this paper, we present a
review of our present knowledge of some of the most pronounced dawn-dusk
asymmetries. We focus on four key aspects: (1) the role of external influences
such as the solar wind and its interaction with the Earth's magnetosphere; (2)
properties of the magnetosphere itself; (3) the role of the ionosphere and (4)
feedback and coupling between regions. We have also identified potential
inconsistencies and gaps in our understanding of dawn-dusk asymmetries in the
Earth's magnetosphere and ionosphere.
