AbstractThis article evaluates the strengths and limitations of field experimentation. It first defines field experimentation and describes the many forms that field experiments take. It also interprets the growth and development of field experimentation. It then discusses why experiments are valuable for causal inference. The assumptions of experimental and nonexperimental inference are distinguished, noting that the value accorded to observational research is often inflated by misleading reporting conventions. The article elaborates on the study of natural experiments and discontinuities as alternatives to both randomized interventions and conventional nonexperimental research. Finally, it outlines a list of methodological issues that arise commonly in connection with experimental design and analysis: the role of covariates, planned vs. unplanned comparisons, and extrapolation. It concludes by dealing with the ways in which field experimentation is reshaping the field of political methodology.