Economics is no longer the "dismal science" dreaded by college freshmen. In recent years, a band of economists has broken away from the charts and graphs of college textbooks, and begun to explain ordinary behavior in plain and often entertaining English. Steve Landsburg was one of the first of the new breed, in his book <I>The Armchair Economist</i> and long-running "Everyday Economics" column in <I>Slate</i> magazine. Now he is back, and more provocative than ever. <P> In <I>More Sex is Safer Sex</i>, Landsburg shows how the rational behavior of each one of us -- when combined together -- produces the often bizarre, seemingly irrational behavior of crowds. We all stand up at the ballpark, so none of us can see. We avoid casual sex, from fear of disease, and we thereby make sex more dangerous. Things really get interesting when Landsburg suggests ways to change the rules, and game the system. Why not charge juries if a convicted felon is exonerated? Why not have each member of Congress represent a national subset of voters, chosen alphabetically? Why not solve the ""overpopulation"" problem by having more children, who will help think of ways to improve our use of resources? <P> <I>More Sex is Safer Sex</i> will make you laugh and argue -- and it will make you think about the world around you in new and unforgettable ways.