After cratonic segments of East Antarctica had already assembled before and within Rodinia supercontinent times, Antarctica remained a centerpiece of the Gondwana supercontinent until its clockwise breakup from Africa, India, Australia, New Zealand and South America from Jurassic to Tertiary times. Most of its continental margins are of rifted, non-volcanic type. Only a short segment was converted from a subduction type to a passive margin after ridge-trench collision along the Pacific side of the Antarctic Peninsula. In recent years, the volume of geophysical data along the continental margin of Antarctica and its conjugate margins has increased substantially, which allows differentiation of the crustal characteristics of its continent-ocean boundaries and transitions. These data and geodynamic modeling indicate that the cause, style, and process of breakup and separation were quite different along the Antarctic margins. An understanding of their processes of formation has consequences for plate-kinematic reconstructions and geodynamic syntheses. As a consequence from rifting and breakup from New Zealand after subduction ceased along its proto-Pacific margin, the West Antarctic Rift System developed as part of the relative motion between East and West Antarctic. The resulting landscape holds the largest sub-marine based ice sheet which plays a role in reconstructing ice sheet dynamics for its role in sea-level changes. Another important role do the Southern Ocean gateways play, where detailed studies of plate kinematics with paleobathymetric modeling enable global paleoclimate simulations.