Why do you fall in love with one person rather than another? With the help of ground-breaking research, Helen Fisher, one of the world's leading experts on romantic love, unlocks the hidden code of desire and attachment. Every one of us, it turns out, primarily expresses one of four broad personality types - Explorer, Builder, Director, or Negotiator - and each of these types is governed by different chemical systems in the brain. Driven by this biology, we are attracted to partners who both mirror and complement our own personality type. Until now the search for love has been blind, but Fisher pulls back the curtain and reveals how we unconsciously go about finding the right match. Drawing on her unique study of 40,000 men and women, she explores each personality type in detail and shows you how to identify your own type as well as explaining why some types match up well, whereas others can prove problematic (Note to Explorers: be prepared for a wild ride when you hitch your star to a fellow Explorer!). Ultimately, Fisher's investigation into the complex nature of romance and attachment leads to astonishing new insights into the essence of dating, love, and marriage. Based on entirely new research-including a detailed questionnaire completed by five million people in thirty-three countries, "Why Him? Why Her?" will change your understanding of why you love him (or her) and help you use nature's chemistry to find and keep your life partner.