In the analysis of center populations at both the national and regional levels considerable use has been made of the rank-size distribution. Within the extensive literature on this distribution, however, there are a number areas that are unclear, neglected, or misleading. Consideration is initially given to the form of the rank-size distribution and to the manner in which it is related to other distributions, notably the Pareto and the lognormal. Attention is also focused on the application of the rank-size distribution to data on center size and on the difficulties that arise in this connection, including the problem of establishing rank-size regularity. The discussion concludes by taking issue with the contention that the rank-size distribution is of relevance in the design and formulation of urban policy.