In this revelatory investigation, science journalist Lydia Denworth takes us in search of friendship’s biological, psychological, and evolutionary foundations. An “expert guide” (Kathryn Bowers, ), Denworth weaves past and present, field biology and neuroscience, to show how our bodies and minds are designed for friendship across life stages, the processes by which healthy social bonds are developed and maintained, and how friendship is changing in the age of social media. Now including a Q&A between the author and her close friend to guide reflection and conversation, is a clarion call for putting positive relationships at the center of our lives.