Contemporary societies are challenged by risks that entail high degrees of complexity, uncertainty and ambiguity – for example, SARS, avian flu, human-induced climate change, diminished genetic diversity, release of persistent toxic substances and terrorism – which cannot be tackled by means of unilateral or simple governmental action. Complex risk issues are further characterised by functional and structural interdependencies between human societies and natural, technological, economic, political, social and cultural systems. They are often a product of profound and rapid technological, economic, social and/or environmental change. Such risks confound traditional political institutions and create unanswered challenges for policy makers within national governments and international bodies. Their negative effects are often pervasive, impacting upon areas well beyond the obvious primary issue areas. Nor do they respect physical boundaries, disciplinary bonds, territorial statehood or political spheres of influence. In many cases, it is a difficult task to detect and to measure the cause-effect relationships inherent to risks and damage. Even experts are uncertain whether a specific set of potential risk candidates will trigger specific adverse effects. There might be other factors, or more likely, an unclear variety of different and uncertain variables, which reduce confidence in the estimated cause and effect chain. Hence, ambiguous evaluations and interpretations emerge, even though based on identical observations or data assessments, and accordingly give rise to scientific and political controversy.