Abstract: Despite the passage of 15 years, Shulman’s (1987) seminal work on pedagogical content knowledge remains important because of the acknowledgement it gives to an old teacher adage: “You don’t know a subject until you’ve taught it.” This bit of folk wisdom suggests that although content knowledge is important for teaching (Anderson, 1989; McDiarmid, Ball, & Anderson, 1989; Ball, 1993) there is a special (and perhaps different) way of knowing that is crucial for effective teaching. Shulman’s introduction to the literature of the term pedagogical content knowledge provided a framework which could allow researchers and scholars to explore more systematically the intuitive notion that expert teachers possess a kind of deeper and richer understanding that permits them to transform more effectively their own knowledge into forms that are accessible to students.