Poverty rates are highest in the most urban and most rural areas of the United States, and are higher in nonmetropolitan than metropolitan areas. Yet, perhaps because only one-fifth of the nation's 35 million poor people live in nonmetropolitan areas, rural poverty has received less attention than urban poverty from both policymakers and researchers. We provide a critical review of literature that examines the factors affecting poverty in rural areas. We focus on studies that explore whether there is a rural effect, i.e., whether there is something about rural places above and beyond demographic characteristics and local economic context that makes poverty more likely in those places. We identify methodological concerns (such as endogenous membership and omitted variables) that may limit the validity of conclusions from existing studies that there is a rural effect. We conclude with suggestions for research that would address these concerns and explore the processes and institutions in urban and rural areas that determine poverty, outcomes, and policy impacts. (Contains 15 footnotes, 3 figures, and 4 tables.) [Support for the preparation of this article was provided by the RUPRI Rural Poverty Research Center, with core funding from the Office of the Assistant Secretary for Planning and Evaluation of the U.S. Department of Health and Human Services; by the Pennsylvania State University Agricultural Experiment Station Project 3501; by the Population Research Institute, Pennsylvania State University, which has core support from the National Institute on Child Health and Human Development (1 R24 HD1025); and by Oregon Agricultural Experiment Station Project 817.]