Least-Cost utility planning confronts utilities with the difficult task of preparing resource plans that use conventional modeling tools in new ways, as in the calculation of avoided costs from production-cost models, and it introduces a new generation of planning tools specifically designed to deal with the complexities of demand-side resource quantification and demand-supply-side integration. In this study, we have provided a road map that seeks to illustrate the broad range of capabilities available with current planning models and the major conceptual distinctions among them. We start from a sketch of the major steps in least-cost planning and highlight some of the complexities involved. We then discuss various approximations to this ideal that can be achieved with existing modeling tools. Moving from the most sophisticated approach, which involves the linking of a number of detailed, specialized models, we discuss successively simpler modeling approaches and the compromises they involve.