The rapid development of wind power that the United States has experienced over the last several years has been coupled with a growing concern that wind development will require substantial additions to the nation's transmission infrastructure. In this report, we review a sample of 40 detailed transmission studies that have included wind power. These studies cover a broad geographic area, and were completed from 2001-2008. Our primary goal in reviewing these studies is to develop a better understanding of the transmission costs needed to access growing quantities of wind generation. A secondary goal is to gain a better appreciation of the differences in transmission planning approaches in order to identify those methodologies that seem most able to estimate the incremental transmission costs associated with wind development. Finally, we hope that the resulting dataset and discussion might be used to inform the assumptions, methods, and results of higher-level assessment models that are sometimes used to estimate the cost of wind deployment (e.g. NEMS and WinDS). The authors and general location of the 40 detailed transmission studies included in our review are illustrated in Figure ES-1. As discussed in the body of the report, these studies vary considerably in scope, authorship, objectives, methodology, and tools. Though we recognize this diversity and are cognizant that comparisons among these studies are therefore somewhat inappropriate, we nonetheless emphasize such simple comparisons in this report. We do so in order to improve our understanding of the range of transmission costs needed to access greater quantities of wind, and to highlight some of the drivers of those costs. In so doing, we gloss over many important details and differences among the studies in our sample.