"One of the current mysteries in Heliophysics is the heating of the solar atmosphere to temperatures that are orders of macagnitude hotter than the solar surface. As a result of this heating, the Sun cannot contain its atmosphere and a continual outflow of plasma streams out from the solar corona to interplanetary space and beyond. For the debate surrounding the exact physical mechanisms of the heating of the corona, we direct the reader to Chapter 6. We here discuss physical mechanisms behind the formation and propagation of the solar wind. The whole volume of space influenced by the solar wind is called the 'Heliosphere' and its size is in part modulated by the solar wind ram pressure. The solar wind extends from the corona to well beyond a hundred astronomical units (AU) to a termination shock. Beyond that shock, the solar wind slows down abruptly in response to the pressure of the interstellar medium, the plasma becomes compressed and more turbulent until it reaches a zone where it can no longer push back the interstellar plasma. In-situ measurements of these outer regions are sparse and our exploration of this boundary layer has only just begun with the Voyager spacecraft. In particular the global shape of the Heliosphere is still not known because the Voyager spacecraft have only measured a very small region of the heliospheric boundary. We direct the reader to Chapter 9 for more detailed information on fascinating region of the Heliosphere"-- Provided by publisher.