THE SOLAR WIND EXPANDS OUTWARD FROM THE SOLAR CORONA AND FILLS THE HELIOSPHERE. IT IS THE MEDIUM BY WHICH SOLAR-DRIVEN SPACE WEATHER PHENOMENA TRANSMIT THEIR EFFECTS TO EARTH AND THE SURROUNDING SPACE ENVIRONMENT. FUNDAMENTAL QUESTIONS REMAIN ABOUT THE WIND'S ORIGIN AND ACCELERATION ITS CONNECTION TO SMALLER-SCALE DYNAMICAL PHENOMENA CLOSE TO THE SUN AND THE PARTITIONING OF THE WIND INTO FAST AND SLOW STREAMS.