In recent years, social scientists have engaged in a deep debate over the methods appropriate to their research. Their long reliance on passive observational collection of information has been challenged by proponents of experimental methods designed to precisely infer causal effects through active intervention in the social world. Some scholars claim that field experiments represent a new gold standard and the best way forward, while others insist that these methods carry inherent inconsistencies, limitations, or ethical dilemmas that observational approaches do not. This unique collection of essays by the most influential figures on every side of this debate reveals its most important stakes and will provide useful guidance to students and scholars in many disciplines.