This paper discusses issues arising from three case studies of the ways people have become tertiary teachers in a polytechnic, a wananga (Maori tertiary institution) and a university in New Zealand. Despite institutional differences, the teachers gained most of their teaching knowledge and skills on the job, learning informally and experientially, and much less through engaging with formal courses or centrally organized educational development activities. Tertiary teachers belong to groupings such as their institution, discipline, department or teaching team that can be seen as communities of practice, and it is in those contexts that their working knowledge and identities as teachers develop. A communities of practice framework in three parts is proposed for supporting and strengthening tertiary teachers' workplace learning and educational development. (Contains 3 notes and 1 figure.)