This article sheds light on the practice and method of expert interviewing in research projects on interest group politics. We first discuss the rationale of interviewing as a data collection instrument, arguing that a careful combination and cross-validation of behavioral and observational data improves the quality of interviews as well as provide a means to validate existing unobtrusive data sources. Moreover, this approach makes it possible to conduct a comprehensive analysis based on both behavioral and observational data sources. Subsequently, we discuss several methodological and practical issues to avoid biases associated with interviewing. One of the key observations from our experience with intereuro is that establishing a robust interview project on the role of interest groups in public policymaking rests largely on careful preparation. Thus, most work needs to be situated before the effective interview takes place, and our key objective is to clarify the importance of this preparatory stage.