This issue of Policy & Politics features a series of articles addressing recent developments in intergovernmental relationships in the advanced Western democracies. There is today, we believe, sufficient uniformity in these developments across different jurisidictions to allow a discussion on the causes, mechanisms and consequences of a new or emerging type of relationship between institutions at different levels. While it is also true that intergovernmental relationships in each individual country are developing to some extent according to the trajectory of institutional relationships which is typical of that national context, we suggest that the triggering mechanisms have been, on the whole, fairly similar across the western world. What we are thus witnessing is a gradual institutional – and inter-institutional – change reflecting both similar problems facing countries in different parts of the world and, at the same time, the trajectory of institutional change in each national context.