Intervention is a central tenet of the various (multitiered) approaches used to implement Response to Intervention (RTI). It appears in Tier 1 core instruction in the form of differentiation, in Tier 2 in the form of supplemental small groups, and in Tier 3 and 4 instruction in the form of more intensive, often individualized support from specialist teachers. Although much is known about particular interventions, less is known about the specific features of interventions necessary for successful teaching and learning. In this article, therefore, the authors examine what they do know about intervention(s) and guide language and literacy professionals in thinking through this critical aspect of a systemic approach to improving literacy outcomes for all students.