Numerous countries are introducing National Qualifications Frameworks (NQFs), or preparing to introduce them, despite the limited empirical evidence for their effectiveness. This paper takes advantage of recent additions to the evidence base on NQFs in order to assess their impacts, focusing on comprehensive frameworks. It also presents analytical tools for studying these impacts, by distinguishing among different types of framework and among the different "change processes" by which they try to achieve their objectives. The evidence, while still inconclusive, shows that the impacts of NQFs have been smaller than expected, have often taken many years to appear, have varied across frameworks and sub-frameworks and have been negative as well as positive. However, the most important conclusion is the variability of the impacts of NQFs and the complexity of the underlying causal processes. (Contains 6 notes and 2 figures.)