Comprehensive measurements of ion spectra, composition, and anisotropies over the energy range ~30 keV to ~5 MeV in Jupiter's foreshock, magnetosheath, and magnetopause were obtained by the low-energy charged particle instrument during the Voyager 1 and 2 encounters with the planet in 1979. Detailed analyses of the spectral and compositional signatures show the following: (1) The ion spectral form at event onset is described well by a power law in energy (dj/dE=KE-&ggr;) over the range ≲100 keV to ~2 MeV; the spectrum becomes generally (but not always) harder at the lower (≲200 keV) energies as the event progresses. (2) The ion spectrum is depleted of protons at E>300 keV and is dominated by ions with Z≥6 (probably oxygen and sulfur) at higher energies; this fact, taken together with the continuity of the spectrum over a factor of ~107 in intensity, suggests that heavy ions (Z≥6) also dominate at low (<300 keV) energies. (3) Spectra of similar form and ion composition are observed inside the magnetosheath and magnetopause. (4) Large (up to 100:1) variable anisotropies are present throughout all events. (5) Events are seen whenever the projection of the interplanetary magnetic field connects the spacecraft to the bow shock. (6) The overall morphology of ion intensity enhancements resembles that observed up-stream of the earth's bow shock in similar energy ranges, including inverse velocity dispersion. These observations lead to the conclusion that ions appearing upstream from Jupiter originate from within Jupiter's magnetosphere. The spectral and compositional features are shown to be consistent with ion escape from the magnetosheath followed by E¿B drift in the solar wind electric field, as suggested by Anderson [1981> for the case of earth. The compositional signatures, together with the large anisotropies and the presence of MeV ions at event onset, preclude the possibility of diffusive, first-order Fermi acceleration upstream of the shock, as has been proposed for the ions observed upstream of earth.