Objective The principles of evidence‐based medicine have been critiqued by the ‘caring’ professions, such as nursing and social work, and evidence‐informed medicine has been proposed as a more client‐centred, integrative approach to practice. The purpose of this study was to explore how Canadian health science librarians who serve nurses and allied health professionals define good service and how they negotiate evidence‐based principles in their searching strategies. Method Twenty‐two librarians completed a 30 minute, semi‐structured phone interview about strategies for providing good service and supporting evidence‐based services. Participants were also asked to respond to three challenging search scenarios. Analysis of results used grounded theory methods. Results Participants’ definitions of good service and strategies for supporting evidence‐based practice involved discussions about types of services provided, aspects of the librarian providing the service and aspects of the information provided during the service. Analysis of search scenarios revealed four justifications librarians rely upon when providing evidence that is in opposition to what their patron hopes to receive (evidentiary, ethical, practice‐based and boundaries of the profession). Conclusion The findings of this study suggest that health science librarians are both constrained and enabled by the principles of evidence‐based medicine and especially by understandings of ‘best evidence’.