Once dominant and institutionalised, the Yakuza, one of Japan's best known criminal organisations, is now shrinking under the combined pressure of legal exclusion, social stigmatisation, and market regulation. Their membership has dropped from more than 80,000 in 2009 to fewer than 20,000 in 2025. Yet their disappearance is far from complete. Based on extensive fieldwork with active and former members, police officers, lawyers, and journalists, Martina Baradel examines how these organisations adapt to repression and explores what happens when a mafia begins to die. 21st Century Yakuza illuminates how Japan's model of regulatory saturation has dismantled the Yakuza's organisational capacity but left behind governance vacuums in markets the state struggles to control. This book demonstrates how the Yakuza persist through symbolic and residual forms of authority even as their formal power erodes, and how their decline has fragmented the criminal underworld. It traces the transformation of the Yakuza from territorially embedded brokers of governance to marginal actors in a more decentralised criminal landscape, including the delegation of trading activities to non-affiliated networks. Through a sharp lens on criminal decline and adaptation, 21st Century Yakuza offers a compelling portrait of a fading underworld and the new forms of disorder emerging in its wake. It is an essential read for anyone interested in the shifting boundaries of law, authority, and illicit power in contemporary Japan.