This publication describes the usage of languages in the multilingual society of Ethiopia. It is based on empirical studies conducted in nine states of the Federal Democratic Republic of Ethiopia in 1997 and 1998. A research team of German and Ethiopian scholars surveyed about 3,500 high school students from 35 Ethiopian towns regarding their language behaviour. The data on the distribution of mother tongues and second languages are published here for the first time and are representative for a typical Ethiopian town. These data outline the development of multilingualism over three generations (students/parents/grandparents) and elucidate factors which promote the spread of multilingualism. The frame for the representation and explanation of the data is an adapted model of the social network theory.