If you are reading this, as a child, you probably went to school to learn. However, as we enter adulthood, we do a great deal of learning informally after we have completed compulsory and formal schooling. Although early theories of learning fell under the quantitative paradigm, new qualitative and social theories of learning have now been proposed. Communities of practice theory can help explain how this informal learning is largely a social endeavor. This theory was developed not as a replacement to existing theories of learning, but as an alternative and complementary explanation of how learning is accomplished. In this paper, I first provide an overview of theories of learning in second language acquisition. Next, I describe these social theories of learning, focusing on communities of practice and how this theory has been applied to research in second language acquisition. I then illustrate how I am applying it to my own research on female foreign language teachers in a professional organization in western Japan.