Relational Frame Theory (RFT) views generalized derived relational responding—relational framing—as the core skill involved in human language. As such, RFT is essential for flexible, fluent conversational skills and academic progress. Our approach to early intervention integrates RFT theory and applied research on the assessment and training of derived relational responding skills with strategies developed by programs which follow a more traditional behavior analytic and specifically Skinnerian analysis of verbal behavior. In this handbook we focus on assessing, establishing, and capitalizing on derived relational responding repertoires in frames of coordination (equivalence), and show you how doing so can promote generalized and generative language repertoires. Throughout this handbook, we identify relational responding repertoires as behavioral cusps to teach towards an ultimate aim of establishing generative language, and present a powerful framework for approaching early intervention, based on RFT and informed by decades of research and practice.