This document provides an overview of liability for environmental damage under international environmental law. It defines liability as legal responsibility for activities that cause harmful environmental damage. There are three types of legal liability: civil, administrative, and criminal. The document also discusses state responsibility for internationally wrongful acts under the 2001 draft articles from the International Law Commission. It examines international liability requirements to pay damages and prevent transboundary harm. A case study on the Trail Smelter case between Canada and the US establishes the polluter pays and prevention of transboundary harm principles.