Since the auto industry’s 2008 crisis, the decades-long trend toward outsourcing by the Detroit Three automakers has stalled. During and after the crisis, original equipment manufacturers moved work inside their corporate boundaries, including the purchase of eight previously spun-off parts plants. Why has this happened? Drawing on 77 interviews in the United States and Canada and 27 insourcing cases, the authors explore how and why insourcing has taken place. Past literature has considered the costs and benefits of creating the vertically integrated corporation, the managerial politics behind vertical disintegration, and the labor–management relations that shape both. While much industrial relations scholarship points to decentralized plant-level partnerships as a union strategy to win investment, the authors find that local unionists are intervening in the politics of the corporation above the plant level to influence the purchasing, manufacturing, and engineering functions that determine the sourcing decision.