Field experiments are experiments in settings with high degrees of naturalism. This article describes different types of field experiments, including randomized field trials, randomized rollout designs, encouragement designs, downstream field experiments, hybrid lab-field experiments, and covert population experiments, and discusses their intellectual background and benefits. It also lists methodological challenges researchers can encounter when conducting field experiments, including failure to treat, selective attrition, spillover, difficulty of replication, and black box causality, and discusses available solutions. Finally, it provides an overview over current and emerging directions in field experimentation and concludes with a brief history of field experiments.