This book demonstrates why and how social activism targeting companies can produce unintended consequences. While it is challenging for social movement organizations (SMOs) to successfully change corporate behavior, it is even more difficult or impossible for SMOs to control the spillover effects of success. Successful social activism affects companies and consumers with diverse interests and intentions beyond the initial target of SMOs, which creates various business opportunities. Entrepreneurs are mobilized by the new opportunities that they identify to initiate their own businesses, and the chain of their actions may produce new market categories unintended by the SMO, including ones that are inconsistent with its superordinate goal. This book explores the process by which an SMO succeeds in changing corporate behavior and how this success leads to unintended market emergence by longitudinally examining the shoe industry in postwar Japan. The Japan Institute of Footwear, a private organization, began advocating shoe functionality over fashion in the 1960s and succeeded in changing corporate behavior in the 1980s through learning by doing; its success led to the unintended emergence of new market categories. The book’s findings offer novel theoretical insights into the relationship between social activism and market change. The analysis also helps us understand the historical context of a movement that emerged in 2019, #KuToo—the word being an amalgam of kutsu (shoes), kutsū (pain), and #MeToo—and to consider its future.