The delineation of an ice sheet grounding line, i.e., the transition boundary where ice detaches from the bed and becomes afloat in the ocean, is critical to ice sheet mass budget calculations, numerical modeling of ice sheet dynamics, ice-ocean interactions, oceanic tides, and subglacial environments. Here, we present 15 years of comprehensive, high-resolution mapping of grounding lines in Antarctica using differential satellite synthetic-aperture radar interferometry (DInSAR) data from the Earth Remote Sensing Satellites 1–2 (ERS-1/2), RADARSAT-1 and 2, and the Advanced Land Observing System (ALOS) PALSAR for years 1994 to 2009. DInSAR directly measures the vertical motion of floating ice shelves in response to tidal oceanic forcing with millimeter precision, at a sample spacing better than 50 m, simultaneously over areas several 100 km wide; in contrast with earlier methods that detect abrupt changes in surface slope in satellite visible imagery or altimetry data. On stagnant and slow-moving areas, we find that breaks in surface slope are reliable indicators of grounding lines; but on most fast-moving glaciers and ice streams, our DInSAR results reveal that prior mappings have positioning errors ranging from a few km to over 100 km. A better agreement is found with ICESat's data, also based on measurements of vertical motion, but with a detection noise one order of magnitude larger than with DInSAR. Overall, the DInSAR mapping of Antarctic grounding lines completely redefines the coastline of Antarctica.