This chapter describes recent theory and research in one limited area of social-cognitive development, namely, the childhood acquisition of knowledge about visual perception. The author and his co-workers have hypothesized that there are two developmental levels of such knowledge. At earlier-developing Level 1, the child understands that others as well as the self see objects, and is also able to infer correctly what objects they do or do not currently see if provided with adequate cues. At later-developing Level 2, the child understands not only that people can see objects, but also that they can have differing visual experiences while seeing the same object; most notably, they can have different spatial perspectival views of it when looking at it from different positions. Arguments and evidence for the developmental distinction between Level 1 and Level 2 knowledge are briefly presented in Section I. A more detailed model of Level 1 knowledge is presented in Section II, together with an account of several studies of its development during the first four years of life. During these early years, children appear to learn a great deal about how to produce visual percepts in others (showing and pointing to things), how to deprive others of percepts (hide objects), and how to diagnose the percepts they currently have (follow others' direction of gaze and pointing gestures). Section III similarly reviews recent theory and research on the development of Level 2 perspective-taking knowledge in older children. This work is focused mainly on the acquisition and use of very general perspective-taking rules, such as the rule that two observers who look at an object array from the same spatial position must on that account necessarily have identical perspectival views of the array. Section IV described further developmental research that could be or is being done on Level 2 knowledge, Level 1 knowledge, and on the Level 1-Level 2 distinction.