The purpose of the study described in this article was to identify the qualities of teaching expertise that correlate with highly effective literacy instruction in grades 6 through 12. Findings draw on survey responses of secondary literacy supervisors at the local school district or state department of education level in every U.S. state. From these responses, 397 characteristics of teaching expertise were analyzed and collapsed into 38 categorical behaviors. After interrater reliabilities were computed, researchers returned to analyze and consolidate the data. This process yielded the following eight domains of secondary literacy teaching expertise: (1) Approaches to teaching (pedagogy); (2) Addressing diverse needs; (3) Personal characteristics; (4) Knowledge base; (5) Approaches to teaching (activities); (6) Professional development; (7) Appropriate relationships with students; and (8) Classroom management. Applications of these data for research, policy, and practice are discussed. (Contains 1 figure and 1 table.)