But what if we could watch entire lives as they unfold through time? What if we could study people from the time that they were teenagers all the way into old age to see what really matters to a person’s health and happiness, and which investments really paid off? For 85 years (and counting), the Harvard Study of Adult Development, which we now direct, has tracked an original group of 724 men and more than 1,300 of their male and female descendants over three generations, asking thousands of questions and taking hundreds of measurements to find out what really keeps people healthy and happy.