Wind offers an alternative energy solution that appears to be environmentally friendly and sustainable, yet considerable uncertainty remains as to the risks and potential impacts on migratory and resident wildlife from construction and operation of wind facilities. Migratory birds and bats, and resident diurnal raptors, are three groups known to be vulnerable to lethal interactions with operating turbines. Preliminary data suggest that impacts to bird populations are not as great as once feared, whereas impacts on bats may have been underestimated. Regardless, the scale and landscape diversity of ongoing and contemplated wind developments worldwide outstrip both available data and our ability to forecast wildlife risks with confidence. Specifically, basic understanding of bird and bat distributions, densities, and movements in relation to a host of key environmental and topographic variables currently are insufficient for accurately estimating risk to individuals and populations across different landscapes or for modeling and predicting cumulative impacts as wind installations proliferate.