In this paper, we present a qualitative case study on an online graduate program for practicing teachers and educators that explores contemporary mathematics and its integration into K to 12 education. Data for the study comprised students' work in the courses, student feedback, and notes from instructor debriefings for two cohorts of the program. The findings are organized in terms of (1) specialized knowledge for teaching mathematics, (2) online professional learning communities, and (3) online teaching in general. We conclude the paper with suggestions for online mathematics teacher education and the identification of venues for future research.