"This article analyzes the reasons for the increase in the number of affiliated workers and the upsurge in the unionization rate in Argentina, in relation to other historical periods, in particular the 90s, in a generalized context of a drop in this indicator in a large proportion of OECD countries. The main question which directs this study is the following: which factors explain the sudden increase in the unionization rate? The answer to this question is part of a series of national and international debates on the definition of union affiliation, its measurement (or its definition), its meaning and particularly the endogenous and exogenous factors that encourage workers to affiliate.The literature recognizes the existence of explanatory factors exogenous to the union, such as economic (Bain and Elsheikh, 1976; Metcalf, 2005; Visser, 2006), political (Wallerstein and Western, 2000; Frege and Kelly, 2003), and judicial institutional factors (Freeman and Pelletier, 1990). As for endogenous factors, these refer to recruitment techniques, and the organizational structure of unions (Undy et al., 1981; Herry, 2006). The information used comes from an inquiry on labour relations carried out by the Ministry of Labour, Employment and Social Security. The sample includes 1,553 businesses, representative of a total universe of 53,038 businesses employing 2,450,400 salaried employees.The research results reveal that even if exogenous judicial institutional factors were stable for decades, the unionization rate nevertheless fell during the 90s, and then went up again beginning in 2003. The main working hypothesis is that this recovery in the unionization rate and the increase in the number of unionized workers are fundamentally due to exogenous factors of a political and economic nature such as support for unionization, the general increase recorded in employment, and the expansion of collective bargaining. "

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