Background: The widespread implementation of longitudinal assessment (LA) to document trainees' progression to independent practice rests more on speculative rather than evidence-based benefits. We aimed to document stakeholders' knowledge of- and attitudes towards LA, and identify how the supports and barriers can help or hinder the uptake and sustainable use of LA. Methods: We interviewed representatives from four stakeholder groups involved in LA. The interview protocols were based on the Theoretical Domains Framework (TDF), which contains a total of 14 behaviour change determinants. Two team members coded the interviews deductively to the TDF, with a third resolving differences in coding. The qualitative data analysis was completed with iterative consultations and discussions with team members until consensus was achieved. Saliency analysis was used to identify dominant domains. Results: Forty-one individuals participated in the study. Three dominant domains were identified. Participants perceive that LA has more positive than negative consequences and requires substantial resources. All the elements and characteristics of LA are present in our data, with differences between stakeholders. Conclusion: Going forward, we could develop and implement tailored and theory driven interventions to promote a shared understanding of LA, and maintain potential positive outcomes while reducing negative ones. Furthermore, resources to support LA implementation need to be addressed to facilitate its uptake.