Written by a geographer, this volume, one in a new series called Turning Points in History, concentrates on the voyages of discovery and their scientific background. Most interesting for the general reader are the lengthy sections dealing with (and demythologizing) Columbus. Against a discussion of medieval cosmography and previous transatlantic navigation (including some thoughts on the Vinland-map controversy), the explorer's early career and three voyages are critically examined. The use of contemporary sources helps convey the excitement of sighting a New World and quickens the work's generally torpid pace. The treatment of the politics of exploration, though covering familiar ground, is also good. Less satisfying is the author's analysis of the impact of the discoveries, whose brevity (few pages) scarcely indicates why the events constituted an historical ""turning point."" It also features some shocking sloppiness. In several paragraphs on the North American settlements, Crone endows the ""American union"" with ""universal free education"" (neither universal nor free in some areas until the 20th century). He congratulates the New England colonists for building up ""six states,"" though one of them (Maine) did not attain statehood until forty years after the Revolution. Disappointing as history, this reference will have to be supplemented by other works for a full picture of the vast changes wrought by the discovery of America.