Work in the design and construction of virtual environments (VEs) is described from the standpoint of semiotic theory. It is advocated that well-constructed visual worlds can create in a person the feelings and cognitions that arise from being in the natural world and that interactions with computer-constructed VEs are mediated through signs. The Human Interface Technology Laboratory at the University of Washington uses VEs for specific instructional purposes and also uses the construction of VEs by students as a way for them to learn content. The design of VEs draws guidance from research in human factors and from the general principles of semiotics. Semiotic theory rests on the proposition that we cannot know the world as it truly is, but only through signs. In the conceptual framework for VEs, knowledge is constructed from information by students. A constructivist learning paradigm was used with 120 seventh and eighth graders who undertook the construction of VE worlds through a process based on semiotic-centered practices. The experiences of these students are described and followed with a discussion of how the sense of presence engendered by VEs can be increased through the manipulation of signs by learners. (Contains 55 references.) (SLD)