This paper describes the evolution of an anecdote-based model of professional development. The nature of professional development is discussed, including case-based instruction and the use of anecdotes. The context for this investigation is presented; this professional development program was targeted to K-12 mathematics teachers who desire to recreate their practice in a manner consistent with mathematics reform initiatives. Through detailed analysis of classroom videotapes, the researchers identified the dimensions around which teachers' practice varies and types of contexts created in classrooms that influence students' opportunities to engage in mathematical thinking and reasoning. Problematic issues identified in teacher discussion sessions were consistent with those identified by the researchers' analysis of classroom videotapes. A set of videotapes that focused on these issues was developed, supplemented with a leader's guide. The suggested steps for working with anecdotes were: share an anecdote; reconstruct the details; view the anecdote again and think of related anecdotes; distill or interpret the issues; identify a personal plan; take to practice; and repeat the cycle with individual teachers' tapes. It was concluded that this model can be applied in a variety of contexts where the goal is to empower professionals to develop and improve their own practice. Contains 16 references. (DLS)