Language spread, or expansion into new geographic and language-use areas, has been studied largely through observation. Thus, discussions of the dynamics of language spread have been based primarily on data obtained through observation. Mark Karan employs a memory span test to evaluate the competence of a large number of subjects in a spreading language, Sango of the Central African Republic. The data from this test are the basis of the author’s statistical studies of the social determinants and predictors of competence in the spreading language. The results indicate the overriding importance of individual motivations for understanding the dynamics of the process of language spread. Based on his findings, Karan presents a framework for discussion, research, and intervention in language spread, along with guidelines for more successful intervention in shift situations. Numerous researchers have linked language spread and language change–language internal modification over time. This quantitative study provides substantive comparison of the two phenomena with data on the distribution of social factors such as age, sex, and education. These distributions are very similar to the distributions of social factors in language change, indicating that language spread and language change are similar processes. Mark Karan earned a Ph.D. degree at University of Pennsylvania in Linguistics in 1996. He did fieldwork in Togo, Benin and Central African Republic. He has served Associate Director of Togo-Benin SIL (1984-1987), Associate Director Central African Republic Academics/Language Programs (1990-2001), and as professor and director of University of North Dakota SIL (1998-2003). Dr Karan is currently the Training Division Director, Academic Affairs, SIL International 2002- .