These days, knitting is, for many, a hobby: We do it to create art, help us relax, and even to explain complex mathematical concepts. Historical knitting, however, was more practical—people knit to clothe themselves or help the troops rather than to relieve stress (although it might have helped there, too). In her new book People Knitting: A Century of Photographs, Barbara Levine has collected more than 100 wonderful images of people from around the world—everyone from cab drivers to nurses to movie stars to First Ladies—knitting for work and for fun. "At the simplest level, the images in this book ... are delightful vintage portraits we can enjoy for their individual charm," she writes in the introduction. "But they reward on another level, too, for they often contain a hint about what the act of knitting has meant personally and culturally at different points in history." Below are a few of mental_floss's favorite photos from Levine's book, accompanied by their captions.