Responding to derived relations among stimuli and events is the subject of an accelerating research program that represents one of the major behavior analytic approaches to complex behavior. Relational Frame Theory: A Post-Skinnerian Account of Human Language and Cognition (Hayes, Barnes-Holmes,& Roche, 2001) offers a conceptual framework for this work and explores its implications for verbal behavior and a variety of other domains of complex human behavior. The authors dismiss Skinner’s interpretation of verbal behavior as unproductive and conceptually flawed and suggest a new definition and a new paradigm for the investigation of verbal phenomena. I found the empirical phenomena important but the conceptual discussion incomplete. A new principle of behavior is promised,but critical features of this principle are not offered. In the absence of an explicit principle,the theory itself is difficult to evaluate. Counter examples suggest a role for mediating behavior,perhaps covert, thus raising the question whether a new principle is needed at all. The performance of subjects in relational frame experiments may be a mosaic of elementary behavioral units, some of which are verbal. If so, verbal behavior underlies relational behavior; it is not defined by it. I defend Skinner’s definition of verbal behavior and argue that an account of relational behavior must be integrated with Skinner’s analysis; it will not replace it.