This chapter discusses the principles of ethnography and participant observation: what they are, how (if) they became standardized as a research method, what form of evidence they constitute, and what place they occupy in the study of Politics. Participant observation has emerged as a popular research tool across the social sciences. In particular, political ethnographies are now widely carried out in a broad variety of contexts, from the study of political institutions and organizations to the investigation of social movements and informal networks, such as terrorist groups and drugs cartels. Political ethnography is also becoming a research method of choice in the field of International Relations. The chapter examines the strengths of ethnographic fieldwork, focusing on issues relating to sampling, access, key informants, and collecting observational data. It also addresses the weaknesses of ethnography, especially issues of subjectivity, reliability, and generalizability.