We posit a case for continuing professional development of teachers that prepares them for 21st century skills, competencies and identities as teachers. The construct of Community of Practice (CoP) is relevant and important for thinking about successful teacher learning. Based on the literature, we propose design tenets for supporting and sustaining communities in the 21st century: foregrounding practice, relying on existing social networks, building on strengths of diversity in membership, task practices that require collaboration and peer and leadership mentoring. We further propose technology architectural considerations for the development of an online learning environment that supports the continual professional development of teachers.