This chapter introduces the main concepts, context, focus, and framework of the book. The centre of analysis concerns the scientific engagement techniques of judges, which refers to a host of practices with which international courts and tribunals assess and interact with the scientific dimensions of environmental disputes. Judicial engagement with science will be evaluated with respect to four distinctive stages of the adjudicatory process, notably, the framing of disputes, the process of scientific fact-finding, causal inquiry, and the standard of review. The scope of this study extends to environmental disputes, broadly understood, which appear in the case law of the International Court of Justice, international arbitral tribunals, regional human rights courts, investment arbitral tribunals, the World Trade Organization dispute settlement bodies, and the International Tribunal for the Law of the Sea. The focus of this book is on the reasoning techniques with which international judges can legitimately justify their choices regarding competing science-based claims.