The Common Core State Standards represent the first standards document to address whether students are able to read progressively more complex texts as they progress across the grades. This article gives an overview of the three components of the model of text complexity that were identified in Appendix A of the Standards and also were the basis for the selection of manuscripts for this special issue: (a) qualitative, (b) quantitative, and (c) reader-task considerations. This introduction gives an overview of the three components and the contributions of the articles in this special issue to extending understanding about these three components.