This paper provides a systematic review of the literature on behavioural decision making in projects. The field is blooming, and given the relevance of decisions in projects and the strong theoretical foundations of behavioural decision making, it offers to contribute to practice and theory in projects and beyond. However, the literature is fragmented and draws only on a fraction of the recent, insightful, and relevant developments on behavioural decision making. This paper organizes current research in a conceptual framework rooted in three schools of thinking—reductionist (on cognitive limitations—errors), pluralist (on political behaviour—lies), and contextualist (on social and organizational sensemaking—misunderstandings). Our review suggests avenues for future research with a wider coverage of theories in cognitive and social psychology and critical and mindful integration of findings and concepts across three schools.