Unions have responded to current membership decline and other organisational problems by restructuring via mergers, increasing union concentration within and across union confederations. A particular noted feature are amalgamations to form 'super-unions'. These conglomerate unions threaten to undermine the role played by confederations in respect of political voice, bargaining coordination, and service provision. Despite these mergers, union pluralism still prevails in many European countries with separate peak associations organised along employment/occupational status or political and religious lines. After comparing the recent merger waves and increased union concentration in western European countries, the consequences for union movements are discussed.Potential strategies for unions to overcome their structural problems have gained increasing attention in recent years. As part of such efforts towards labour movement 'revitalisation', the issues of mobilisation and restructuring are particularly relevant. Last year's annual review (Ebbinghaus, 2002b) concentrated on the challenge of deunionisation; this year, the analysis will be concerned with strategies for organisational change. In order to mobilise and retain members, unions have in some countries become increasingly dependent on 'union securities' provided by the welfare state such as sheltered public sector employment, statutory workplace access, union-run unemployment insurance, involvement in social concertation and the selfadministration of social insurance. Unions have had varying success in organising the new workplaces, innovative sectors, atypical employment groups, and the rising female labour force as well as young people. Some of the challenges facing unions are