Industrial accidents causing water pollution, including those with large-scale and transboundary effects, can occur anytime and in any country, no matter how stringent the safety standards. The devastating effects of such accidents on humans and the environment, both within and across countries, have been demonstrated by past major accidents in the United Nations Economic Commission for Europe (UNECE) region. These accidents were tragic reminders that it is often impossible for the country where an accident happens to respond alone. Therefore, effective cooperation at the international level and, more importantly, between neighbouring states is of utmost importance, not only to respond to industrial accidents affecting transboundary waters but also to prevent and prepare for them.