Central to reaching peace and settlement in Northern Ireland was a sequence of British–Irish intergovernmental discussions and negotiations, dating from the beginning of the 1980s. British and Irish state cooperation and intervention has remained central to the stability of the settlement reached in 1998. The motives of state actors, however, have been unclear, and the role of the state in the political process has been the subject of some scholarly controversy. This paper looks at the types of evidence that can help to resolve such questions. It focuses on the value of elite interviews, arguing that they can constitute an important and irreplaceable body of evidence when used critically, but it also highlights the risks of excessive reliance on this type of source. It goes on to describe a major research project in University College Dublin whose aim was to record the experiences and interpretations of the actors who engaged in British–Irish negotiations over the last four decades. It discusses the resulting elite interviews and witness seminars and the methodological and ethical difficulties encountered. It describes how these were overcome, and outlines the conditions of confidentiality imposed.