The sustainability challenges we face today are greater than any we have previously confronted. This year, the United Nations adopted the 2030 Agenda for Sustainable Development, which includes 17 Sustainable Development Goals. Law is a necessary part of the solution to sustainability challenges. To achieve sustainability goals, appropriate and well-implemented legal frameworks and tools must be in place. And, importantly, they must be effective. And to ensure thatlaws work, we must first understand what makes law effective. What factors contribute to its design, implementation, outcome and ultimate impact? And what can we do to improve it? This publication represents a valuable initial effort to take on these questions, through empirical assessment and analysis. The framework it presents is a versatile tool for researchers to structure their study of the effectiveness of law for sustainability. The case studies demonstrate use of the framework, and also provide important insights and information about the effectiveness of environmental law in particular countries and contexts.