OBJECTIVE: To highlight the importance of sampling and data collection processes in qualitative interview studies, and to discuss the contribution of these processes to determining the strength of the evidence generated and thereby to decisions for public health practice and policy. APPROACH: This discussion is informed by a hierarchy-of-evidence-for-practice model. The paper provides succinct guidelines for key sampling and data collection considerations in qualitative research involving interview studies. The importance of allowing time for immersion in a given community to become familiar with the context and population is discussed, as well as the practical constraints that sometimes operate against this stage. The role of theory in guiding sample selection is discussed both in terms of identifying likely sources of rich data and in understanding the issues emerging from the data. It is noted that sampling further assists in confirming the developing evidence and also illuminates data that does not seem to fit. The importance of reporting sampling and data collection processes is highlighted clearly to enable others to assess both the strength of the evidence and the broader applications of the findings. CONCLUSION: Sampling and data collection processes are critical to determining the quality of a study and the generalisability of the findings. We argue that these processes should operate within the parameters of the research goal, be guided by emerging theoretical considerations, cover a range of relevant participant perspectives, and be clearly outlined in research reports with an explanation of any research limitations.