A new, complete velocity field from satellite remote sensing is combined with numerical modeling to infer the rheology of the Larsen B Ice Shelf before its disintegration. The resulting spatial distribution of the flow parameter exhibits large variability, which reflects very well observed ice shelf features. This variability is explained by factors including advection of colder ice from tributary glaciers, bottom melting, and the presence of zones of strong shear and fracture. The inferred distribution is applied to simulate numerically the flow regime of the ice shelf and to examine its modification by the presence of open rifts and by the retreat of ice shelf front between 1996 and 2000. Results demonstrate that variable rheology is essential to understanding ice shelf evolution, especially the close relationship among frontal retreat, fracture, ice flow acceleration, and the destabilization of ice shelves.