This chapter describes the use of field research for development of psychological theory. Field research helps identify which phenomena are most psychologically and behaviorally consequential. The chapter focuses on the kinds of theoretical insights afforded by research in field settings. It explains what one means by field research as opposed to laboratory research, and discusses advantages that come from finding and testing ideas in the field. Observational methods can be put to many important uses in field settings. The chapter examines the experimental research in the field that is explicitly designed for the purpose of comparison and causal inference. It explores the range of theoretical goals that can be accomplished with field research. The chapter outlines the strengths and weaknesses of various field research techniques and best practices of each one. It concludes with practical suggestions and reasons for researchers at various stages of experience to engage in field research.