If intelligent computer programs are to represent and reason about mental states and processes, a critical first step is to characterize the content to be represented. Toward that goal, I sketch an outline of a folk psychology of one important mental process, attention. The everyday knowledge people have about their own and others’ attentional processes is characterized in a number of generalizations, based mostly on common sense rather than systematic empirical study. One set of generalizations concerns the basic phenomenon of attention--the focus of mental activity on one thing at a time. Another set of generalizations relates to knowledge about what determines the focus of attention. People’s implicit knowledge about the determinants of attention includes an understanding of the relationship between attention and effort, as well as an appreciation for the variety of stimuli that can capture or maintain attention without effort. A further set of generalizations concerns the consequences of attention. Here it is argued that people have 'implicit knowledge about attention’s effects on perception, memory, and action. Finally, some concluding remarks concern the development of knowledge about attention, differences between folk and empirical-scientific psychologies of attention, and possible applications for representations of knowledge about attention.