What forms of knowledge are relevant for political decisions? How can expert knowledge influence policy - is this even possible? Rational-modernized societies, including the countries of the European Union, consider it particularly important that decisions affecting large sections of the population are supported by expert opinions. Experts and science have a much better reputation than politics: while politics represents interests, it is up to the supposedly objective expert knowledge to ensure neutral, i.e. non-interest-led decisions. This book examines the role of expert knowledge in eight EU countries. The case studies from the EU research project "Knowledge and Policy" prove that politics cannot work in any other formats than political ones: This means that scientific knowledge cannot directly influence political decisions, as both politics and science speak a different "language". It is only possible for external knowledge to be processed for political purposes via detours and several intermediary bodies.