Abstract Background: OncotypeDx is a prognostic and predictive genomic assay used in early-stage hormone receptor–positive, HER2− (HR+/HER2−) breast cancer. It is used to inform adjuvant chemotherapy decisions, but not all eligible women receive testing. We aimed to assess variation in testing by demographics and geography, and to determine whether testing was associated with chemotherapy. Methods: For 1,615 women in the Carolina Breast Cancer Study with HR+/HER2−, Stage I–II tumors, we estimated prevalence differences (PD) and 95% confidence intervals (CI) for receipt of OncotypeDx genomic testing in association with and sociodemographic characteristics. We assessed associations between testing and chemotherapy receipt overall and by race. Finally, we calculated the proportion of eligible women receiving OncotypeDx by county-level rurality, census tract-level socioeconomic status, and Area Health Education Center regions. Results: 38% (N = 609) of potentially eligible women were tested, with lower testing prevalences in Black (31%; PD, −11%; 95% CI, −16%–6%) and low-income women (24%; PD, −20%; 95% CI, −29% to −11%) relative to non-Black and higher income women. Urban participants were less likely to be tested than rural participants, though this association varied by region. Among women with low genomic risk tumors, tested participants were 29% less likely to receive chemotherapy than untested participants (95% CI, −40% to −17%). Racial differences in chemotherapy were restricted to untested women. Conclusions: Both individual and area-level socioeconomics predict likelihood of OncotypeDx testing. Impact: Variable adoption of OncotypeDx by socioeconomics and across geographic settings may contribute to excess chemotherapy among patients with HR+/HER2− cancers. See related In the Spotlight, p. 635