By all accounts, open source communities are overwhelmingly male (over 95%, according to a recent GitHub survey) and predominantly white. Collecting data on diversity in open source communities is challenging in and of itself. The Diversity & Inclusion in Scientific Computing (DISC) program at NumFOCUS, with support from the Moore Foundation, this year launched a project to begin measuring diversity and inclusion metrics at open source scientific computing conferences around the world, with the goal of identifying and disseminating best practices for inclusion. In this talk, I explore the unique challenges of tackling diversity & inclusion issues in open source communities, the paradoxical fact that open source participants are extraordinarily homogenous, and the practices and procedures open source communities and projects must adopt to promote greater diversity and inclusion.