On attending a conference on the Jovian satellites at UCLA, I heard Lou Lanze­ rotti vigorously present the exciting data on the sputtering of water ice by Me V protons taken with W. L. Brown at AT&T Bell Labs. In his inimitable way he made clear that this new electronic sputtering process was very poorly under­ stood and was very important for surface properties of sattelites. I was immedia­ tely hooked, and have been working ever since with Lanzerotti, Brown, my col­ league at Virginia, John Boring, and Bo Sundqvist at Uppsala on understanding the ejection of material from surfaces and applying laboratory results to intere­ sting planetary problems. In the course of writing this book I also had the benefit of spending a semester with the Planetary Geosciences group in Hawaii, thanks to Tom McCord, a period of time with Doug Nash at JPL, and a period ot time with the group at Catania. The book was started with the encouragement of Lou Lanzerotti. The writing has gone slowly as the field has been changing rapidly. Even now I feel it is incom­ plete, as the interesting Halley dust data have just recently been interpreted in detail, Voyager has recently visited Neptune, and the data on Pluto are rapidly improving. However, most of the principles for plasma ion alteration of surfaces and gases have been established allowing, I hope, a coherent and useful frame­ work for incorporating both new laboratory and planetary data.