We report on the development and validation of the TEX-IN3, a research tool and protocol designed to assess the quality of the classroom literacy environment. The TEX-IN3 is described in terms of its theoretical base as well as its practical applications. The TEX-IN3 includes three basic components: a text inventory, a text "in-use" observation, and a series of text interviews. The validation of the TEX-IN3 is first reported in terms of its content, development, and focus. Next, a validation study examining the relationship between the TEX-IN3 and student growth in reading comprehension is described. The findings from this study offer support for all three components of the instrument as associated with student achievement growth.