Research SummaryWe investigate family CEO birth order as an antecedent of family firms' CSR behavior. Despite psychology literature recognizing it as a key predictor of individual behavior, birth order has been largely neglected in management research. Drawing on behavioral economics and evolutionary psychology—specifically, the Family Niche Model—we identify economic and social preferences as two competing channels through which birth order effects propagate to CSR behavior. An unbalanced panel dataset of 550 firm‐year observations from 84 family firms between 2010 and 2022 reveals a negative relationship between family CEO birth order and CSR behavior, pointing to the dominance of the economic channel, whereby the higher risk tolerance among later borns manifests. This relationship is positively and negatively moderated by family CEO sibship size and age, respectively.Managerial SummaryWe examine the role of family CEO birth order in shaping family firms' CSR behavior considering that individuals' economic and social preferences are strongly influenced by their birth order. The results show that family CEO birth order negatively relates to CSR behavior. We argue that this relationship is driven by higher risk tolerance among later‐born family CEOs, who are consequentially less inclined to adopt CSR behavior as a risk‐mitigating strategy. The relationship is attenuated by family CEO sibship size and amplified by CEO age. Our study cautions family firms concerned with CSR to carefully consider the implications of birth order when selecting family members for the CEO position. Concurrently, family CEOs should be aware that their early family experiences may affect their CSR decisions.