The focus of this study was to understand knowledge flows among teachers by examining what types of knowledge was shared by teachers, as well as what motivates or hinders teachers to share knowledge online. We examined an electronic mailing list (listserv) supporting a community of practice of literacy teachers. Data were gathered on the teachers in the listserv through online observations. Additional data were collected through semi-structured telephone interviews with 20 teachers. Findings suggest that two motives of community involvement--collectivism, and principlism appear to be the main motivators for knowledge sharers to share knowledge, while lack of knowledge and competing priority appear to be the main barriers. Practical implications for knowledge sharing and suggestions for future research are discussed. The findings of this study inform teachers, listserv moderators, teacher associations, as well as researchers of educational technology who are interested in knowledge sharing among teachers within communities of practice mediated by computer networks.