Purpose: This paper aims to analyze how the legitimacy of the policy of external quality assurance (EQA) in Colombian higher education has evolved over the past 30 years through an examination of its two main instruments: the compulsory control of minimum quality standards for academic programs and institutions (registro calificado) and accreditations of excellence for programs and institutions. Design/methodology/approach: Based on the methodology of process-tracing, this paper offers a review of the main sequences of the policy of EQA in Colombian higher education: the origins (1990-1998), the expansion (1998-2011) and the contestation (2011-2021). In each sequence, the sources of the substantive and procedural legitimacy of the policy are analyzed. This analysis is based on qualitative data comprising semi-structured interviews with key informants, online information from the 2011 and 2018 student protests and official documentation. Findings: The policy of EQA in Colombian higher education had relatively high levels of substantive and procedural legitimacy during the first two sequences. However, the situation has become more ambivalent since 2011. On the one hand, internal contradictions and student movements' growing criticism of neoliberal policies have undermined some of the foundations of this policy. On the other hand, higher education institutions and the Colombian Government still have a positive perception of EQA and have recently revisited the policy to address some of its shortcomings. Originality/value: From a conceptual standpoint, this paper advances our understanding of how quality assurance in higher education gains, sustains or loses legitimacy by discussing and testing typologies of legitimacy in the analysis of a national system of EQA. From an empirical perspective, this paper provides a diachronic analysis of EQA in Colombian higher education, a case that has primarily been studied through a technical-rational perspective.