This article provides an overview of the legitimacy and the legitimacy crises of the World Health Organization (WHO). During the COVID-19 pandemic, in the era of social media, WHO’s legitimacy crisis has appeared to be historically strong. Based on previous quantitative and qualitative research, the article assesses factors influencing the legitimacy of the WHO. The article identifies the most significant legitimacy crises of the WHO, and examines the similarities and differences between the crises. The legitimacy crises of the WHO are intertwined with infectious disease epidemics. In these situations, the WHO, with its measures and recommendations, becomes under public scrutiny due to increased media visibility. Moreover, the WHO gets merged into international and national political struggles. With the COVID-19 pandemic, research on the legitimacy of the WHO is timely and necessary. Through this comprehensive overview of the WHO, it is also possible to assess the impact of institutional legitimacy crises on the effectiveness and acceptability of global governance