This chapter analyzes the case of the Frente Amplio (Broad Front, FA) in Uruguay as an unusual organization. Since its founding, the FA has exhibited a dual structure: a coalition of various factions that compose the party and a movement comprising a common grassroots structure (Base Committees). The latter is not necessarily affiliated with any particular faction and it participates in all of the party’s decision-making structures. The FA fulfills the essential functions required to qualify as a political party. These functions manifest themselves in the participatory processes that develop the party’s electoral platforms and also control the nomination of presidential candidates. More critically, the coalition and the grassroots movement tended to influence the policy decisions of the party’s parliamentary caucus when the FA was an opposition party, as well as the decisions of the executive branch when the FA was in government (2005–20). In this process, grassroots party activists exercised significant influence over political decisions that were particularly sensitive for the Left. Regarding vertical interest aggregation, the FA has developed strong, informal links with various social actors, especially with labor unions.