Spacecraft such as the Pioneer, Vela, and Voyager have explored the interplanetary medium between the orbits of Mercury and Pluto. The insights derived from these missions have been successfully applied to magnetospheric, astro-solar, and cosmic ray physics. This book is an overview of these insights, using magnetohydrodynamic (MHD) flows as the framework for interpreting objects and processes observed in the interplanetary medium. Topics include various types of MHD shocks and interactions among them, tangential and rotational discontinuities, force-free field configurations, the formation...