This resource paper on geographical spatial diffusion is part of a series designed to supplement undergraduate geography courses. Focusing on the unfolding of man's patterns over geographic space and through time, the paper provides the basic theoretical background of this new, rapidly growing area of geography. Following a short introductory section, chapter two outlines the various carriers and barriers to both physical and cultural diffusion. Carrier processes may take the form of expansion, relocation, hierarchical filtering, or contagious diffusion as with diseases. Barriers to diffusion may be physical or cultural, such as differences in languages or levels of technology. Since spatial diffusion takes place on many different scales, chapter three focuses on the various models of individual or micro-level diffusion, urban diffusion, regional diffusion, and macro-level (or national and international) diffusion. Chapter four discusses the frontiers of diffusion research. Also included is a list of further readings and illustrative references. (Author/DE)