Radio astronomy has been expanding into outer space so fast in recent years that it is pleasant to find our own solar system at last receiving the attention it deserves. In this session we are concerned with everything within the system except the sun and our own planet. I start with a question, to which I shall return later: Where does the sun end? In another session you will hear of the experiments on the far-out parts of the solar corona; here we are concerned with interplanetary space as well as with the planets themselves, and what lies within this region may or may not be considered part of the solar corona.