This article discusses aspects of the informal learning of tertiary teachers in a polytechnic, a wananga (Maori tertiary institution) and a university in New Zealand. Case studies showed that they gained their teaching knowledge and skills mainly on the job, through informal, experiential learning, and much less through formal courses, professional development or familiarity with the literature of learning and teaching: that teaching knowledge was mainly tacit and procedural, rather than propositional. The case studies also showed that the contexts in which teachers worked, such as their institution, department or programme team, were significant. This article argues that, since informal learning was shown to be so important, a "community of practice" framework may be a useful new approach for supporting the development of teachers' working knowledge and identities. (Contains 1 figure and 2 notes.)