High standards of academic conduct, including the awareness raising of plagiaristic behaviours, are regarded as a central part of the development of individual scholarship in higher education systems worldwide. This research contributes to original knowledge in relation to understanding how students develop an understanding of plagiarism and how they actualise it within their undergraduate programmes in Thailand. Data were collected through a survey, numerical modelling and interview, and the Theory of Planned Behaviour is adopted as a lens through which the issues are interpreted and explored. The findings expose in detail not only the inadequacy of students' understanding of both the gravity and complex and extensive nature of plagiarism but also their motivations for engaging in plagiaristic behaviour, which mainly centred upon lack of control and confidence in their academic endeavours. The study has implications for practitioners and administrators in higher education, particularly in relation to explicit expectations of students' academic conduct.