Why do people who have dogs live happier, longer, and more fulfulling lives? Sociologists and veterinarians have spent years investigating the positive effects that dogs have on people's health and happiness yet their findings are inaccessible to ordinary people, hidden in obscure journals to be shared with other experts.

Now the international bestselling author of the 100 Simple Secrets series has collected the most current and significant data from more than a thousand of the best scientific studies on the profound relationship between humans and our canine companions. These...