Investments in public health workforce development are based on the assumption that capacity and competencies are linked with the effectiveness and efficiency of providing essential public health services. However, evidence of the effects of workforce quantity or quality on the performance of core public health functions is limited. A review of public health, health care, and teacher education literature was conducted to determine the state of research in the field and to identify promising approaches and study designs for application to public health workforce training. A total of 861 articles and abstracts were reviewed from the health literature and 470 from teacher education literature. Sixty-five reports in the public health or health care literature and 68 in the education literature met the inclusion criteria. Eleven studies in public health or health literature reported positive correlations and 3 determined no substantial correlation to credentials. In the education literature, 10 studies reported a positive link, whereas 9 studies reported mixed or nonsignificant results. We conclude that a paucity of quality research or compelling evidence exists linking certification or credentialing to any related outcome. Until further research is conducted, discussions on the need for public health workforce certification and credentialing will be based on good-faith expectations for improving individual and organizational performance.