Little is known about what inspires students to be involved in their doctoral process and stay persistent when facing challenges. This study explored the nature of students' engagement in the doctoral work. Altogether, 21 behavioural sciences doctoral students from one top-level research community were interviewed. The interview data were qualitatively content analysed. The doctoral students described their engagement in terms of experiences of dedication and efficiency. They rarely reported experiences of absorption. The primary sources of their engagement in their thesis work were increased sense of competence and relatedness. In addition, three qualitatively different forms of engagement in doctoral work including adaptive engagement, agentic engagement and work-life inspired engagement were identified from the doctoral students' descriptions. Further, there was a variation among the students in terms of what forms of engagement they emphasised in different phases of their doctoral studies. This study contributed to the literature on doctoral student engagement by opening the nature of engagement at the interfaces of studying and working by shedding light on the dual role of doctoral students as both students and professional researchers. Moreover, this study broke down the complexity of engagement by identifying qualitatively different experiences and sources of engagement. The results encourage designing such engaging learning environments for doctoral students that promote their experiences of being competent researchers and integrated into their scholarly community.