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The current work reports 2 experiments that investigate the development of false belief from the perspective of Relational Frame Theory. The true and false belief test protocol used across both experiments contained a range of tasks that involved responding in accordance with the 3 perspective-taking frames of I-YOU, HERE-THERE, NOW-THEN, and in accordance with logical NOT. Experiment 1 involved the presentation of a protocol containing 10 true/false tasks to participants of 5 age groups ranging from 3 to 30 years old. Experiment 2 was identical to Experiment 1, except that the number of tasks presented in the protocol was increased to 60 and novel participants were employed. The results of both experiments indicated a developmental trend in which accuracy on the protocol appeared to increase as a function of age. Furthermore, the fact that neither study indicated a statistically significant effect for trial type suggested that responding to both true and false belief may involve overlapping behavioral processes. The findings are discussed in terms of their implications for Relational Frame Theory, behavior analysis, and the mainstream developmental literature on understanding true and false belief..