This article examines occurrences of the mental quality clear “comprehension” or clear “knowing” (sampajañña/samprajanya) in early Buddhist discourse with a view to discerning its function in relation to the meditative cultivation of mindfulness. These two terms occur often together, pointing to a collaboration between the more bare or receptive awareness provided by mindfulness and the cognizing or recognizing function fulfilled by clear knowing. Such collaboration can apply to a range of different contexts, from daily life activities, including sleeping, to deep states of concentration and the cultivation of insight into impermanence and emptiness. The understanding that emerges in this way might contribute to a better appreciation of the functions of mindfulness both on its own and in relation to other mental qualities closely associated with it, in the way this was understood in different periods of Buddhist thought.