A consensus has been emerging during the past several years that illicit trafficking of nuclear materials is a problem that needs a more focused international response. One possible component of a program to combat illicit trafficking is nuclear forensics whereby intercepted nuclear materials are analyzed to provide clues for answering attribution questions. In this report we focus on international cooperation that is specifically addressing the development of nuclear forensics. First we will describe the role of the Nuclear Smuggling International Technical Working Group (ITWG) in developing nuclear forensics, and then we will present some specific examples of cooperative work by the Institute for Transuranium Elements of the European Commission with various European states. Recognizing the potential importance of a nuclear forensics capability, the P-8 countries in 1995 encouraged technical experts to evaluate the role of nuclear forensics in combating nuclear smuggling and possibly developing mechanisms for international cooperation. As a result, an International Conference on Nuclear Smuggling Forensic Analysis was held in November, 1995, at Lawrence Livermore National Laboratory to investigate technical cooperation on nuclear forensics. The International Conference provided a unique mix of scientists, law enforcement, and intelligence experts from 14 countries and organizations. All participants were invited to make presentations, and the format of the Conference was designed to encourage open discussion and broad participation.