Self-agency is a crucial aspect of self-awareness. It is underresearched given the phenomenon's subjectivity and difficulty of study. It is particularly underresearched comparatively, given that animals cannot receive agency instructions or make agency declarations. Accordingly, we developed a distinctively new self-agency paradigm. Humans and rhesus macaques learned event categories differentiated by whether the participant's volitional response controlled a screen launch. They learned by trial and error after minimal instructions with no agency orientation (humans) or no instructions (monkeys). After learning, humans' verbalized category descriptions were coded for self-agency attributions. Across three experiments, humans' agency attributions qualitatively improved discrimination performance-participants not invoking self-agency rarely exceeded chance performance. It also produced a diagnostic latency profile: classification accuracy depended heavily on the temporal relationship between the button-press and the launch, but only for those invoking agency. In our last experiment, monkeys performed the launch task. Their performance and latency profiles mirrored that of humans. Thus, self-agency can be self-discovered as a frame organizing discrimination. And it may be used as a discrimination cue by some nonhuman animals as well. (PsycInfo Database Record (c) 2021 APA, all rights reserved).