This paper examines the concepts of validity and legitimacy in accounting knowledge from a critical and societal perspective, with particular attention to Global South contexts and Latin America. Challenging dominant technical and regulatory conceptions, it conceptualises accounting as a socially embedded practice whose authority is historically constructed, institutionally mediated and politically contested. Drawing on alternative accounting theories and critical social theory, the study integrates genealogical analysis, communicative rationality, symbolic power and theories of social justice to explain how accounting knowledge becomes accepted as legitimate. Building on Foucault's notion of regimes of truth, the paper shows how accounting standards and practices acquire authority through power-knowledge relations rather than neutral technical superiority, a dynamic especially visible in the transnational diffusion of accounting models in Latin America. Habermasian insights are used to problematise the dominance of instrumental rationality in accounting regulation and to highlight deficits in communicative validation. Bourdieu's concept of symbolic capital explains how epistemic authority is consolidated within the accounting field, while theories of recognition and justice developed by Honneth and Fraser provide normative criteria for assessing the societal consequences of accounting practices. The paper argues that accounting legitimacy cannot be reduced to regulatory compliance or academic consensus. Instead, particularly in Latin American societies marked by inequality and institutional hybridity, legitimacy should be understood as a societal achievement grounded in social recognition, justice and contextual relevance.