SDI is in political ebb, but books about it are in flow-all without our knowing exactly what it is. Of the edited volumes, that by Wells and Litwak is the best, with a relatively brief introduction that sets SDI in the context of both history and American offensive force modernization. Charles Glaser's chapter and the ensuing panel discussion on the problem of transition are especially interesting. The Cimbala volume, most of whose authors are of more conservative bent, is strongest in its treatment of point defenses. The Guerrier and Thompson volume is a source book, with short analyses and statements of position by political figures, for and against SDI. Daalder has the benefit both of single authorship and of being a European who knows American strategy well. He understands strategy but gives primacy to politics. This long essay is the best discussion of SDI and Europe so far.