Background: The introduction of efficacious physical activity (PA) interventions in routine primary health care (PHC) is a complex process. Understanding factors influencing the process can enhance the development of successful introduction strategies. Purpose: The aim of this qualitative study was to explore stakeholders’ perceptions on factors influencing the introduction, i.e., adoption, implementation, and continuation, of PA interventions in PHC. Method: Twenty-eight semistructured interviews were held with intervention managers, PHC advisors, intervention providers, and referring general practitioners of five PA interventions delivered in PHC. A theoretical framework on the introduction of innovations in health care was used to guide the data collection. Influencing factors were identified using thematic analysis. Results: Stakeholders reported preconditions for the introduction of PA interventions in PHC (e.g., support, resources, and networks and collaborations), in addition to characteristics of PA interventions (e.g., compatibility, flexibility, and intervention materials) and characteristics of PHC professionals (e.g., knowledge, positive attitudes, and beliefs about capabilities) perceived to enhance the introduction process. Furthermore, they proposed strategies for the development of PA interventions (e.g., involvement of future stakeholders, full development, and refinement) and strategies to introduce PA interventions in PHC (e.g., training, assistance, and reinforcement). The majority of the influencing factors were discussed specifically in relation to one or two stages. Conclusion: This study presents an overview of factors that are perceived to influence the introduction of PA interventions in PHC. It underscores the importance of taking these factors into account when designing introduction strategies and of giving special attention to the distinct stages of the process. © 2014, International Society of Behavioral Medicine.