In this seminar I will introduce Behavioural OR (BOR) as a burgeoning area of specialisation within the OR discipline, whose main purpose is to provide more accurate descriptions of how people behave in OR-supported settings, with a view to informing the design and deployment of effective OR interventions. After surveying the relevant literature covering a 30-year period between 1989 and 2018, I will distinguish two types of studies, variance and process, each concerned with different research questions exploring the extent to which behaviour hinders or enhances the use of OR. I will argue that coordinating the pluralistic insights from the two approaches can help to better understand the behavioural dimension of OR-supported activity, as well as offer useful guidance for the practice of OR. I will conclude the seminar with some suggestions for further developing the BOR agenda, including the use of modelling as a way to bridge the gap between variance and process approaches for studying behavioural issues in OR-supported settings.