Commerce and menstruation from the twentieth century to today. The menstrual product industry has played a large role in shaping the past hundred years of menstrual culture, including technological innovation, creative advertising, and education in classrooms. How much do we know about this sector and how has it changed in later decades? What constitutes “the industry,” who works in it, and how is it adapting to the current menstrual equity movement?  Cash Flow provides a new academic study of the menstrual corporate landscape that links its twentieth-century origins to the current day. Drawing on a range of previously unexplored archival materials and interviews with industry insiders, each chapter examines one key company and brand: Saba in Norway, Essity in Sweden, Tambrands in the Soviet Union, Procter & Gamble in Britain and Europe, Kimberly-Clark in North America, and start-ups Clue and Thinx. The book provides timely insights into a secretive and largely unexamined corporate world and the ongoing political and industry-wide debate about the cost of menstrual products. Cash Flow will be of interest to a wide range of groups within and outside academia, including scholars in the emerging field of critical menstruation studies and menstrual activists.