In seeking to evaluate the efficacy of post-9/11 homeland security expenses - which have risen by more than a trillion dollars, not including war costs - the common query has been, 'are we safer?' This, however, is the wrong question. Of course we are 'safer' - the posting of a single security guard at one building's entrance enhances safety. The correct question is, 'are any gains in security worth the funds expended?' This book applies risk and cost-benefit evaluation techniques to answer this very question.