Abstract: For the past eight summers, educators from around the world have joined together in the affinity space of #CyberPD – a participant-driven professional book study hosted on a variety of platforms including individual blogs, Google+ Community, Twitter, Padlet, and Voxer. This paper considers in what ways the #CyberPD event could be viewed as an affinity space and how the characteristics of a nurturing affinity space (Gee & Hayes, 2012) contributed to the educators’ participation. My purpose was to build an understanding of the ways voluntary, participant-driven online professional learning for educators can be a useful and effective form of professional development.