In this article, the author discusses small learning communities (SLCs), a term that is used to refer to the practice of organizing secondary schools into smaller units. Features of SLCs include small structure, curricular specialization and choice, a focus on the learner and learning, and, in particular, the active and collaborative nature of teachers' and students' work. Five interrelated spheres of activities are key to transforming traditional comprehensive high schools into effective SLCs: (1) building- and district-level support; (2) interdisciplinary teaching and learning teams; (3) rigorous, relevant curriculum and instruction; (4) inclusive programs and practices; and (5) continuous program improvement. For administrators looking to implement SLCs, it is important to remember that small size is not an end in itself--in order for them to succeed, administrators, counselors, and special education staff members must cease to operate at the school level and instead operate at the level of the SLC. (Contains 1 figure.)