1. Introduction.- 1.1 Why the “Inner Heliosphere”?.- 1.2 Scientific Objectives and General Aspects of the Helios Mission.- 1.3 Scientific Highlights and Summary.- 1.4 Heliospheric Physics and Some Astrophysical Connections.- References.- 2. Remote Sensing Observations of the Solar Corona.- 2.1 Introduction.- 2.2 Morphology of the Outer Corona: A Brief Survey.- 2.3 Coronal Plasma Density.- 2.4 Coronal Magnetic Structure.- 2.5 Coronal Velocities and Turbulence.- 2.6 Coronal Mass Ejections.- 2.7 Appendix: Radio-Sounding Measurement Techniques.- References.- 3. Large-Scale Structure of the Interplanetary Medium.- 3.1 Introduction.- 3.2 Longitudinal Stream Boundaries.- 3.3 Latitudinal Stream Boundaries.- 3.4 Stream Structures with Respect to the Heliomagnetic Equator.- 3.5 Corotating Shock Waves.- 3.6 Scenario in Terms of the “Ballerina Model”.- 3.7 The Solar Wind as a Two-State Phenomenon.- 3.8 Variations During the Solar Activity Cycle.- 3.9 Conclusions and Outlook.- References.- 4. The Interplanetary Magnetic Field.- 4.1 Introduction.- 4.2 Radial Variations.- 4.3 The Solar Magnetic Field and the Interplanetary Magnetic Field.- 4.4 Summary and Outlook.- References.- 5. Interplanetary Dust.- 5.1 Introduction.- 5.2 Methods of Observation.- 5.3 Particle Properties.- 5.4 Physical Processes.- 5.5 Mass and Size Distribution.- 5.6 Spatial Distribution.- 5.7 Orbit Distribution.- 5.8 Compatibility of Dust Experiments with Zodiacal Light Observations.- 5.9 Sources and Sinks.- 5.10 Attempt at a Judgement.- References.