This is the first in a series of articles addressing conceptions of teacher learning, and the implications of these conceptions for improving the practice of teaching. This article provides descriptions of three perspectives on teacher learning: knowledge-for-practice, knowledge-in-practice, and knowledge-of practice (Cochran-Smith & Lytle, 1999). Examples of the application of each of these conceptions of teacher learning from the special education literature are provided. In subsequent articles, the implications of each of these perspectives are addressed relative to pre-service teacher education, professional development, research and the application of research to practice, and school change/improvement. A final article then addresses the application of the knowledge of practice conception of teacher learning to the practice and preparation of principals, as they provide leadership in facilitating teacher learning in local schools.