Ageism, defined as stereotypes, prejudices, and discrimination based on age, is a pervasive phenomenon across individuals, settings, historical periods, and cultures. To address the universality of ageism, we explore three main questions: (a) Does ageism happen throughout the course of a person's life? (b) Does ageism permeate all spheres of life? (c) Does ageism exist all around the world? We conclude that although ageism is universal, there are substantial variations in its definition, manifestations, and impact over time and in different sociocultural contexts. The variability identified suggests that we cannot use a one-size-fits-all approach to conceptualize or target ageism, but instead we should adopt a personalized approach, which considers the sociocultural context, the personal attributes of the targets and agents of ageism, and the normative framework concerning ageism at the global and local levels. This title is also available as Open Access on Cambridge Core.