The aim of this chapter is to introduce readers to ethnographic fieldwork including participant observation and ethnographic interviews. Ethnographic fieldwork is a robust research methodology for studying patients’ experiences and perspectives and, therefore, particularly valuable for health technology assessment (HTA). Furthermore, it leads to important insights that are relevant to patient involvement in HTA. Following the introduction, the chapter is divided into seven sections. First, we briefly introduce ethnographic research in relation to patient involvement in HTA. The next three sections focus on participant observation, ethnographic interviewing, and field notes as an important research activity in ethnographic fieldwork. Subsequently, we consider the analytical process. We close the chapter with a discussion of knowledge production within ethnographic fieldwork and some concluding remarks.