Book excerpt: This safety guide represents an international consensus and understanding on principles for intervention and numerical values for generic intervention levels. It became clear during the Chernobyl Project that there was a need for clarification of the international guidance on intervention and, moreover, for a simple set of internally consistent intervention levels having some generic application internationally. The recommendations in this publication are the basis for the standards and numerical guidance related to intervention contained in the International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources (jointly sponsored by FAO, IAEA, ILO, OECD/NEA, PAHO and WHO).