The introduction outlines the book’s two main puzzles: First, why is legalistic governance emerging in South Korea and Japan, which were long known for their non legalistic regulatory styles? Second, what accounts for the varieties of legalism observed in Korea and Japan? Legalism describes a style of regulation that relies on more formal, detailed, and enforceable laws and regulations, as well as more participatory policy design and implementation processes. This book argues that activists and lawyers are often-overlooked societal drivers behind the emergence of legalism and the broader judicialization of politics in Korea and Japan.