In the first decades after mass production, between 1913 and 1939, middle-class Americans not only bought cars but also enthusiastically redesigned them. By examining the ways Americans creatively adapted their automobiles, Tinkering takes a fresh look at automotive design from the bottom up, as a process that included manufacturers, engineers, advice experts, and consumers in various guises. Franz argues that automobile ownership opened new possibilities for ingenuity among consumers even as large corporations came to control innovation. Franz weaves together a variety of sources, from serial fiction to corporate documents, to explore tinkering as a form of authority in a culture that valued ingenuity. Women drivers represented one group of consumers who used tinkering to advance their claim to social autonomy. Some canny drivers moved beyond modifying their individual cars to become independent inventors, patenting and selling automotive accessories for the burgeoning national demand for aftermarket products. Earl S. Tupper was one such tinkerer who went on to invent Tupperware. These savvy tinkerers worked in a changing landscape of invention shaped increasingly by automotive giants. By the 1930s, Ford and General Motors worked to change the popular discourse of ingenuity and used the world's fairs of the Depression as a stage to promote a hierarchy of innovation. Franz not only demonstrates the entrepreneurial spirit of American consumers but she engages larger historical questions about gender, consumption and ingenuity while charting the impact corporate expansion on tinkering during the first half of the twentieth century.