Throughout the industrialised world trade unionists are reforming their organisations as part of a strategy to adjust to new labour market, economic and political circumstances. This volume examines the role of merger activity in this process of reform. The book identifies the pattern of merger activity, the factors that promote its development and its impact on union structure and governance. Most merger activity is shown to originate in some adverse environmental change, such as membership decline. Furthermore, there is little evidence to suggest that mergers have improved union performance in the recruitment, retention and organisation of members, although, in some cases, the reform of systems of membership participation has been facilitated. The shift away from industrial unions has been accelerated by merger involvement, which has also brought into question the role of confederations where the number of affiliated unions has declined markedly. The book comprises two sections. The first section examines the merger process in ten countries (Australia, Austria, Denmark, Germany, Greece, Norway, Portugal, Sweden, UK and US). The second section comprises three ‘horizontal’ chapters in which authors of the national chapters develop themes that emerge from the national chapters in comparative perspective.