Antarctica was a center-piece of the Gondwana supercontinent. About 85 percent of Antarcticas 10000 km long continental margins are of a rifted divergent type, and about 1200 km have been converted from a subduction-type to a passive margin after ridge-trench collision along the Pacific side of the Antarctic Peninsula. The separation of South America, Africa, India, Australia and New Zealand from Antarctica and the creation of a continuous Southern Ocean began in the Jurassic and continued until the mid Tertiary. In recent years, the amount of geophysical data along the continental margin of Antarctica has increased substantially, which allows to differentiate the crustal characteristics of its continent-ocean boundaries and transitional zones (COB/COT). The data and geodynamic modelling indicate that the cause, style and process of breakup and separation are highly variable along the Antarctic margin. A circum-Antarctic map summarizes the crustal styles of the margin and the location and geophysical characteristics of the COT. Definitions and identifications of the COT and an understanding of its process of formation have consequences for plate-kinematic reconstructions, geodynamic syntheses and isostatic considerations.