Administrators play a critical role in teachers' professional development. An ambitious approach focuses on content, process, and context to ensure continuous improvement at the individual, collegial, and organizational level.Quality professional development for teachers has never been more important than it is today as the challenges they face intensify and the expectations for quality education increase. The nation's education reform agenda of increasing teacher effectiveness and student achievement requires teachers to learn new skills and perspectives while simultaneously unlearning practices and beliefs that have dominated their work for years (Darling-Hammond and McLaughlin 1996). Principals, as school leaders, must have an ambitious vision of professional development. Profesional development is broader in scope than staff development and includes such informal activities as reading professional publications, attending professional meetings, and even viewing television specials related to an academic discipline.Teachers have historically participated in professional development activities inside and outside schools. These activities have been sponsored by a variety of organizations, including schools, school districts, consortia of districts, professional organizations, teacher associations, state departments of education, private consultants, and institutions of higher education. They have most typically taken the form of inservice training, workshops, conferences, summer institutes, and graduate courses.Data on professional development as practiced in the mid-1990s indicate that more than 80 percent of teachers participated in workshops or inservice training in their assigned teaching area that was sponsored by schools, school districts, or affiliated organizations (National Center for Education Statistics, NCES, 1998). In addition, about half of these teachers participated in activities sponsored by professional associations and about a quarter enrolled in college or university courses (NCES 1998).A recent study by NCES (1999) reports that 99 percent of teachers surveyed in 1998 had participated in at least one of eight different professional Tom Ganser is director, Office of Field Experiences, University of Wisconsin, Whitewater. He is also a consultant in the design, implementation, and evaluation of mentor programs for teachers, including mentor training and workshops for beginning teachers. Correspondence concerning this article may be sent to gansert@mail.uww.edu.