Background: The Swedish ambulance health care services are changing and developing, with the ambulance nurse playing a central role in the development of practice. The competence required by ambulance nurses in the profession remains undefined and provides a challenge. The need for a clear and updateddescription of ambulance nurses’ competence, including the perspective of professional experiences, seems to be essential.Aim: The aim of this study was to elucidate ambulance nurses’ professional experiences and to describe aspects affecting their competence.Methods: For data collection, the study used the Critical Incident Technique, interviewing 32 ambulance nurses. A qualitative content analysis was applied.Results and conclusion: This study elucidates essential parts of the development, usage and perceptions of the competence of ambulance nurses and how, in various ways, this is affected by professional experiences.The development of competence is strongly affected by the ability and possibility to reflect on practice on a professional and personal level, particularly in cooperation with colleagues. Experiences and communication skills are regarded as decisive in challenging clinical situations. The way ambulance nurses perceive their own competence is closely linked to patient outcome. The results of this study can be used in professional and curriculum development.