Professional development for teachers is a continuous process of individual and collective examination of practice. This publication first identifies reasons why traditional staff development often fails and several prerequisites for effective professional development. These include establishing real stakes for students; providing incentives for teachers to take the risks inherent in changing practices; convincing educators that proposed changes are substantial and not merely fads; and implementing policies that create a foundation for a safe and orderly learning environment. Nine principles of effective professional development are then presented: (1) professional development should ensure depth of content knowledge; (2) it should provide a strong foundation in the pedagogy of particular disciplines; (3) it should provide more general knowledge about teaching and learning processes and about schools as institutions; (4) it should be rooted in and reflect the best available research; (5) it should contribute to measurable improvement in student achievement; (6) it expects teachers to be intellectually engaged with ideas and resources; (7) it provides sufficient time, support, and resources to enable teachers to master new content and pedagogy and to integrate these into their practice; (8) it should be designed by representatives of those who participate in it, in cooperation with experts in the field; and (9) it should take a variety of forms, including some not typically considered. (ND)