Aim and design: This study explores causes for professionalization in Swiss national sport federations (NSFs). We conducted a multiple-case study employing a qualitative approach with interviews and documents from seven NSFs. A three-level framework guided the analysis in distinguishing NSFs endogenous causes, and causes in their external and internal environment.Results: Causes for professionalization were widely similar in the NSFs. Conflicts on the board, un-clear decision-making competences and initiatives of key persons have prominently triggered pro-fessionalization, particularly for differentiation of strategic boards and executive headquarters, spe-cialization and paid staff. The Swiss government, Swiss Olympic Association and sponsors (external environment) have brought about considerable adaptations in NSFs’ strategies, accountability issues and commercialization, whereas expectations of NSFs’ member organizations (internal environment) have had little impact on their professionalization in general. Rather, the NSFs view them as neces-sities they themselves do not perceive. Our analysis revealed additional NSF-specific factors (e.g., popularity, financial resources, attitude of individuals towards professionalization) that have an im-pact on pace and continuity of the process once it has been initiated.Conclusion: Our analysis is a first step towards understanding the professionalization process in Swiss NSFs. Referring to the similar causes for professionalization, uncertainty and competing for resources may have led some NSFs to mimic those NSFs they deem successful, leading to similar conditions that call for professionalization (e.g., with respect to workload and internal expectations). Respective networks between motivated people in the NSFs and stakeholders could support a de-liberate professionalization. NSFs endogenous and NSF external causes for professionalization seem to be reciprocal. This should be considered more specifically in the analysis of professionalization in NSFs. Single-case studies would be useful to understand the mechanisms and eventual phases more clearly, to identify eventual barriers and avoid unintended consequences to, finally, support NSFs’ professionalization in an efficient manner.