This paper presents the behaviourist “non-normative” Peace Research (PR) tradition with two objectives. One objective is to locate this field in relation to closely related fields of research. PR specificity is: the dependent variable of peace and conflict when compared with Political Science and International Relations; the normative concern with the causes of war when compared with Strategic Studies; and the rejection of the “practicality” of research and a restraint on normativity when compared with Peace Studies (defined as peace research, peace teaching and peace action) and Conflict Resolution. Also, PR is considered here as one of the sub-fields of International Security Studies. The second objective of the paper is to present the history of PR. Since its creation in the 1950s, with a focus on inter-state conflict as an alternative to Strategic Studies, PR had two defining periods: one in the late 1960s labelled as the “socialist revolution”, with the conceptualisation of peace as more than the absence of war (positive peace) and a challenge for normativity in research; and a second period in the 1980s that brought the broadening of the referent object to intra-state conflict and liberal peace, and the emergence of other social sciences dedicated to the study of issues in, or close to, PR, broadly defined as security with some of them adopting a normative stance in research. The epistemological community of PR kept its behaviourist approach in spite of these two normative challenges, and its distinctiveness and unity is much due to its method.