The use in recent years of evaluation practices within audit bodies to support accountability arrangements has become more extensive, wide-ranging, and complex. In doing so, it has stretched the framework within which accountability arrangements operate and, just as putting new wine into old leather bottles stretches the old leather until the bottle breaks, there is the danger that the same might happen to old accountability arrangements. This chapter explores the consequences of introducing evaluation practices into audit bodies and asks whether existing institutional arrangements are being stretched to their breaking point. We use the U.K.’s National Audit Office (NAO) to illustrate the argument, but the intention is to make wider claims relevant to the important interface between the worlds of evaluation and accountability.