The theory of comparative federalism asserts that federations require a second chamber for the representation of regional interests in central law-making. Yet there has been little systematic analysis of the contribution of second chambers in parliamentary federations to this task. The main purpose of this book is to demonstrate to what extent the two strongest parliamentary second chambers, the Australian Senate and the German Bundesrat are linked to the federal structures in which they are embedded. The study analyzes the contribution of the members of these second chambers in advancing interests that are linked to the regional constituents whom they represent or to the collective fiscal or administrative interests of a regional government with whom they are associated. The analysis underscores the largely ‘executive’ character of intergovernmental relations in parliamentary federations, a feature that corresponds with the composition of the German Bundesrat, but not of the Australian Senate. In the concluding chapter some preliminary observations are made as to whether our findings also generate interesting insights for the larger group of parliamentary second chambers in federal or quasi-federal states, such as the Belgian, Spanish and Canadian Senates, the UK House of Lords and the Indian Raiya Sabha.