To explore emergency nurses' and physicians' experience of collaboration and collective decision-making when triaging older Emergency Department patients within the interprofessional team triage system. Qualitative. Semi-structured interviews were conducted with seven nurses and five physicians. Transcripts were analysed via Interpretive Description between September 2016-May 2017. 'Negotiating collaboration' was developed as the main theme. Three subthemes influenced the negotiation process: Participants described divergent opinions on how an optimal triage system should work ('preferences for triage systems'); they had conflicting perceptions of each profession's role ('role perceptions'); and they expressed different coping strategies regarding 'perceived time pressure'. The compatibility of participants' views on these sub-themes determined whether the nurse and physician were able to successfully negotiate their collaboration. These themes became more evident when the team triaged older ED patients. Improving interprofessional team triage requires working with the involved nurses' and physicians' values and beliefs. The strengths of both professions need to be considered and a flexible approach to collaboration established according to the patients' situations. Emergency Department leaders need to consider nurses' and physicians' values and beliefs to promote interprofessional collaboration in team triage.