MHD-based models have shaped our expectations on the boundary between the solar wind and interstellar space. Predictions of the location of the termination shock (TS) in particular have ranged over the years from ～5 to > 100 AU, depending on the choice of parameters inserted into the force balance equation. Voyager 1, however, has now crossed the TS foreshock at ～85 AU (Krimigis et al, 2003) and the TS itself at ～94 AU (Decker et al, 2005a). Salient characteristics of this newly discovered region are as follows: (a) Solar wind speed is substantially reduced as the TS is approached, decreases to ～100 km/s on crossing and drops to 0 ± 50 km/s several weeks later. (b) Intense anisotropic beams of energetic ( > 40 keV) ions, apparently field-aligned, are flowing tangentially to the radial direction and dominantly outward away from the sun. (c) Relativistic electrons are present concurrently with the ions, and exhibit similar intensity-time profiles, (d) Ion composition is characteristic of anomalous cosmic rays (ACR) but spectra are power laws at lower ( < 50 MeV total energy) energies and still exhibit a "hump" (at ～10 and ～30 MeV/nuc, for O and He, respectively), an ACR characteristic, (e) The plasma β is > 1 past the TS foreshock and well into the heliosheath. (f) The power law spectral index at E < 20 MeV is ～1.7, resulting in a shock compression ratio of ～2.25, i.e. a relatively weak shock. The low energy part of the spectrum, however, is unlikely to be the product of diffusive shock acceleration (large anisotropies) and may well be due to pickup ions (Gloeckler et al, 2005).
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