Although Skinner's "Verbal Behavior" (1957) was published over 50 years ago, behavior-analytic research on human language and cognition has been slow to develop. In recent years, a new behavioral approach to language known as relational frame theory (RFT) has generated considerable attention, research, and debate. The controversy surrounding RFT can be difficult to fully appreciate, partly because of the complexity of the theory itself and partly because the debate has spanned several years and several journals. The current paper aims to provide a concise overview of RFT and a summary of key points of debate and controversy.