Despite widespread and growing public interest in sustainability certifications, many social entrepreneurs have opted not to obtain such certification. Drawing on recent studies highlighting the salience of both gender and context in shaping differences among social enterprises, we develop an identity-based framework for explaining heterogeneity in the adoption of sustainability certification. We test our ideas using a sample of 1251 U.S. firms obtained from B Lab, the organization responsible for assessing Certified B Corporations. Our results show that woman-owned businesses are twice as likely to qualify for certification and more than three times as likely to certify. Moreover, this propensity to certify is amplified in contexts where sustainability norms are weak, mimetic pressure to obtain sustainability certification is low, and woman-owned businesses are less prevalent. These findings support our central theoretical argument that certification differences are due to actors' efforts to engage in identity work, strengthening their sense of self-coherence and distinctiveness by way of this authentication process. We conclude by highlighting our contributions to existing scholarship on social entrepreneurship, identity work, and certification adoption, as well as strategic implications for B Lab.