What are the essential qualities of a great relationship? What do people in healthy and happy relationships do differently? Scientists and academics have spent entire careers investigating the nature of relationships, dating, and marriage, yet their findings are inaccessible to ordinary people, hidden in obscure journals read only by other academics. Now the bestselling author of the 100 Simple Secrets series has collected the most current and significant data from more than a thousand studies on relationships and spells out the key findings in plain English. The advice is not based on one person's unique experiences or opinions, but offers for the first time the research of noted scientists studying the lives and loves of average Americans. Each of the findings is accompanied by a true story that shows the results in action.