The frictional strength of ice seems to be well below that for all other rocks. Triaxial testing of cylinders of pure water ice containing a 45¿ inclined sawcut, at temperatures of 77≤T≤115 K and confining pressures 0.1≤P≤250 MPa, reveals the frictional laws &tgr;=0.20 &sgr;n+8.3 MPa for P≥10 MPa and &tgr;=0.55 &sgr;n+1.0 MPa for P≤5 MPa, where &tgr; and &sgr;n are the shear and normal stresses on the sawcut surface. Friction is independent of T and, over the one order of magnitude tested, of average sliding velocity. The sliding behavior is invariably stick slip. Examination of sliding surfaces shows only minor gouge development. A curious arrangement of densely packed short vertical fractures occurs primarily in samples with anomalously low strength. These results apply to models of near-surface tectonic activity on Jupiter's three large icy moons, Europa, Callisto, and Ganymede. They indicate, for example, that a global expansion on Ganymede of 3 linear percent will cause extensional movement on preexisting faults at depths to 7¿3 km. ¿ American Geophysical Union 1988