A multidisciplinary exploration of our human inclination to herd and why our instinct to copy others can be dangerous in today's interlinked world. Rioting teenagers, tumbling stock markets, and the spread of religious terrorism appear to have little in common, but all are driven by the same basic instincts: the tendency to herd, follow, and imitate others. In today's interconnected world, group choices often seem maladaptive. With unprecedented speed, information flashes across the globe and drives rapid shifts in group opinion. Adverse results can include speculative economic bubbles, irrational denigration of scientists and other experts, seismic political reversals, and more. Drawing on insights from across the social, behavioral, and natural sciences, Michelle Baddeley explores contexts in which behavior is driven by the herd. She analyzes the rational versus nonrational and cognitive aspects of this phenomenon.