[The genesis of the Family Health Support Center (NASF) in the primary healthcare agenda in Brazil].

The article reports on the sociogenesis of the Family Health Support Center (NASF) in Brazil, based on document analysis and 16 in-depth interviews with key informants. Based on triangulation of data and sources and with Pierre Bourdieu as the theoretical reference, a sociohistorical analysis was performed to build a timeline of events related to the formulation of the NASF, including conflicts, interests, alliances, and agreements to allow the proposal's implementation. Four moments were identified in the history of the NASF: from 2000 to 2002, the first discussion for building a proposal to expand the family healthcare (PHC) teams; from 2003 to 2005, drafting a proposal to expand the core team, with the design centered on curative and individual interventions (NAISF); from 2005 to 2006, the repeal of the Brazilian Ministry of Health ruling that established the first proposal, revealing a "vacuum" in the debate on the expansion of PHC teams; and from 2007 to 2008, when the NASF was created with the central purpose of inter-consultation support activities with the family health teams. The genesis of the NASF resulted from a favorable situation in Brazil's political and institutional context, featuring important linkage with members of the government administration and pressure on the Ministry of Health from professional societies and municipal health administrators. The two proposals (NAISF and NASF) were designed differently, although both aimed to expand the scope of practices and case-resolution capacity in PHC. The analysis of the policy's genesis allowed understanding possible repercussions on the policymaking process in ambiguities that are still present in NASF practices.