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Cognitive control is often viewed as an ability or as an interaction between higher and lower level systems. This article takes an instance perspective, articulating the view that cognitive control is accomplished by a multiplicity of specific acts of control tailored to accomplish specific adjustments to the cognitive system in specific circumstances. Acts of control take states of the cognitive system and states of the world as inputs, perform computations, and produce changes in the state of the cognitive system as output. Acts of control take measurable time. They are voluntary and specific, and they can be learned. The article addresses acts of control for inhibiting responses, shifting attention, and switching tasks, describing how to measure their durations and assess whether they are voluntary and specific. It concludes by reconciling ability, interactive systems, and instance perspectives and considering implications for research and practice.