Multi-level governance is a fairly new concept, that has however travelled well in modern political science. The status of the concept remains a bit unclear, mainly because it tries to grasp quite a set of (mutually linked) societal and institutional changes, as well as changes in policy style and policy outputs. We try to use multi-level governance as a heuristic tool, and we focus on the potential consequences of the changes that it describes. Four types of consequences are briefly discussed. First we look at efficiency, at the way in which and the degree in which complex institutions can produce policy paralysis. Secondly we deal with representation and accountability, discussing the meaning of these concepts in multilayered settings. Then we look at the way in which territorial representation seems to (re)gain importance as a result of the erosion of the borderlines between domestic and international polities. And finally we look at the way in which legitimacy of politicalauthorities and policies can be organized within the framework of multi-level governance. The other articles of this special issue all deal in more detail with one or more of these four types of consequences of multi-level governance.