This Article is the first to examine age diversity in the legal literature, mapping out its descriptive, normative, and legal dimensions. Age diversity is a plural concept, as heterogeneity of age can take many forms in various human institutions. Likewise, the normative rationales for these assorted age diversities are rooted in distinct theoretical foundations, making the case for or against age diversity contextual rather than universal. A host of legal rules play a significant role in regulating age diversity, influencing the presence of different generations in the workplace, judiciary, and Congress. Better understanding the nature and consequences of age diversity allows us to recognize the unique set of costs and benefits it entails and enriches our understanding of other forms of difference. Further, examining the law with an age diversity lens highlights fruitful avenues for legal reform in fields as varied as immigration law, employment law, and the law of juries. In an era of increased inter-generational tension and a rapidly aging population, the time is ripe to evaluate age diversity and the law’s role in shaping it.