This article presents a theory of the cross‐sectional fertility differential, which produces the negative wage–fertility relationship based on job heterogeneity. Although evidence suggests the importance of job heterogeneity in the labor market, it has largely been ignored in theories of fertility choice. I show that a theory incorporating job heterogeneity requires only standard conditions on preferences to generate the negative wage–fertility relationship, and the negative relationship derived from the model is robust to changes in economic environments (e.g., public policy and technology). Furthermore, the theory reconciles the negative cross‐sectional wage–fertility relationship with various time‐series variations in aggregate fertility.