Teacher educators need tools to help them think about teacher learning, to design activities and programs that foster it, and to assess the results of their work with preservice and in-service teachers. In this article, in order to improve the conceptual tools available for the design and study of teacher education, the author teases apart distinctions among several popular notions of teacher community, clarifying how each can make a distinct contribution to the research and practice of teacher development. The author also suggests how activity theory in general, and writing about third spaces in specific, might compliment the contributions and limitations of various notions of teacher community. (Contains 3 tables.)