<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Contribution:</i> This study contributes to efforts to diversify the field of engineering by studying the influence of co-curricular activities on African American students’ development of key nontechnical professional skills. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Background:</i> The 21st Century workforce requires significant collaboration and communication. For engineering graduates to meet workforce challenges, they must graduate with nontechnical skills. This study operationalized these skills using traits identified in the National Academy of Engineering’s (NAE) “Engineer of 2020” report. The NAE also points to the urgent need for the United States to diversify its workforce; broadening the participation of African American engineers is key to doing so. Co-curricular activities help students develop nontechnical professional skills and are particularly important to African Americans at predominantly White institutions (PWIs). <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Research Question:</i> How do African American engineering students attending PWIs in the United States develop nontechnical professional skills through participation in ethnic-specific co-curricular activities? <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Methodology:</i> This qualitative study explored the lived experiences of 16 participants from one of six engineering disciplines. Each participant was a member of at least one of the following organizations: a Black fraternity or sorority (termed Black Greek Letter organizations), their campus student chapter of the National Society of Black Engineers, or an institution-sponsored program for racially underrepresented students such as a minority engineering program. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Findings:</i> Data analysis revealed significant evidence that involvement in one or more of the studied ethnic-specific co-curricular activities enhanced African American engineering students’ educational experiences by providing resources and opportunities to help them develop professional skills.