When local officials consider how best to maximize efficiency in local government, one often-discussed proposal is the consolidation of city and county services. In theory, consolidation should produce economies of scale which allows cost savings to be achieved - average costs are reduced when spread out over a wider set of users. The reality is that this may not always occur -- but why? Why do city-county consolidations not always produce cost savings and, in some case, actually lead to higher costs? To help local and state officials grappling with this issue, we have summarized recent literature on the causes of diseconomies of scale in city-county consolidations and listed useful online resources.