This report discusses research-supported principles and practices in the professional development of bilingual education teachers and teachers of language minority students, illustrated with the experiences of a number of specific projects. An introductory section offers background and the philosophy of the study. Subsequent sections address principles of effectiveness and promising practice (an overview of projects with promising practices, new teacher recruitment and preparation, continuing professional education, and provision of a context supporting professional growth); present descriptions of 12 professional development projects; examine specific challenges in design and implementation (competing constituent goals, quality control, institutionalization of practices, and effects of projects on the minority language community); and discuss policy implications (professional standards, the role of federal support, contributions of project team stability, integration of new ideas across content, partnership of local education agencies and higher education institutions, and the importance of language resources). Contains a list of references and site contacts. (MSE)