From movie plots to ad campaigns to viral videos, if they feature twins, they grab our attention every time. But it’s not only the general public who are fascinated with twins. Over many decades, twins have garnered attention from psychologists and other researchers because of what they can tell us about how our genes and environment interact to make us who we are. Nancy Segal, PhD, talks about the state of twin research today and what we've learned about twins, and from them, over the decades.