Maps of the distribution of lunar surface magnetic fields produced by the electron reflection method have shown that the largest observed concentrations of lunar crustal magnetization occur antipodal (diametrically opposite) to 4 relatively young large impact basins: Imbrium, Orientale, Serenitatis, and Crisium. A model is proposed here for the formation of these magnetization concentrations (or 'magcons') in which the partially ionized vapor cloud produced in a hypervelocity (>10 km s-1) basin-forming impact expands around the moon forcing a pre-existing ambient magnetic field to be concentrated for a brief (<1 day) time period in the antipodal zone. Acquisition of magnetic remanence during the period of compressed field amplification may occur by one of several mechanisms including shock remanence by impact of solid secondaries ejected from the basin-forming event. The model implies that basin-forming impacts have played a major role in determining the large-scale distribution of crustal magnetization detectable from lunar orbit. ¿ American Geophysical Union 1987