This paper describes the three types of nonformal and informal professional development provided by teachers' organizations. The first type is a minimal approach, the second focuses on contextual variation and teacher diversity, and the third consists of informal learning opportunities developed by teachers themselves. The article identifies strategies for improving the "fit" between available professional development and teachers' occupational needs. Rather than recommending a single, "best" professional-development strategy, the paper emphasizes sociological and organizational factors germane to teachers' organizations themselves, such as the teacher organizations' role in teacher socialization, the demographics of teacher organization participation, and internal structural features. These factors suggest that teachers' organizations must look within at a variety of organizational issues and consider a wide variety of organizational strategies simultaneously. The report draws from conceptual and empirical research on national, state/provincial, and local teacher union reform activities; on teachers' perceptions of their organizations; and on teachers' past involvement with their organizations. It examines the tradition of teacher professional development and concludes by suggesting that teachers' organizations move away from policies of discrete and limited professional development events to consider a variety of organizational sites as potentially useful for teacher learning. (RJM)