The heliospheric boundary region and its inward and outward effects

The solar wind is separated from the interstellar medium (ISM) by a complex interaction region. Observed precursors combined with theoretical considerations indicate that Voyager 1 might reach and cross the termination shock of the supersonic solar wind around the end of the century, the actual time of transit depending both on the somewhat uncertain physical state of the local interstellar medium and on dynamical pressure variations of the solar wind. An in-situ study of the interaction region is thus now in sight. Processes in the interaction region have important effects both inwards, toward the inner heliosphere, and outwards, toward the outer heliosheath and the interstellar medium. A better understanding of those processes is important both for heliospheric studies and for long-standing problems of the modulation and origin of galactic cosmic rays. Recent results on the heliospheric derivatives of neutral gas penetrating through the boundary region from the local interstellar medium will also be discussed.