Introduction: Uncertainty is understood as an important component of the information seeking process, but it has not been explored as a component of reference and information service. Method: Interpretative phenomenological analysis was used to examine the practitioner perspective of reference and information service for eight academic research librarians in the United States. Analysis: Data were analyzed thematically according to interpretative phenomenological analysis procedures. Results: Variety and uncertainty emerged as one of the themes of experience for these practitioners. Based on the results of this study, a conceptual model is proposed for uncertainty in reference and information service. Conclusion: The conceptual model of uncertainty in reference and information service can be used for further study of the phenomenon and to contribute to a comparative sociology of uncertainty across professions. In addition, it can be used to support practitioners and to better prepare students for the uncertainties of practice. [This paper was published in: "Proceedings of ISIC: The Behaviour Conference" (Leeds, England, Sep 2-5, 2014), Part 2, Paper isicsp9.]