Working Paper 33989 DOI 10.3386/w33989 Issue Date July 2025 This paper considers why fertility has fallen to historically low levels in virtually all high-income countries. Using cohort data, we document rising childlessness at all observed ages and falling completed fertility. This cohort perspective underscores the need to explain long-run shifts in fertility behavior. We review existing research and conclude that period-based explanations focused on short-term changes in income or prices cann...