Most of the contributions published in this volume were prepared within the framework of the research project "Dynamics of Contacts between Populations and Languages - Lexical and Structural Diffusion and the Genealogies in the Sahel" co-ordinated at the Faculty of Humanities, Charles University in Prague, and in a workshop dedicated to the project at the occasion of the XVIIth International Congress of Linguists (Prague 2003).The purpose of the project was to examine the linguistic situation in the Sahel in view of the recent developments in the study of language contacts, assessing the reality of the Sahel "Sprachbund". The concept of "Sprachbund", or 'linguistic area' as a bundle of features common to languages over a geographical area has experienced considerable extention: from phonology and morphology, its domain has been extended to morphosyntax and lexicon. By doing so, the concepts of calquing, typological convergence, reflexification and metatypy are being used to characterize the process witnessed in the study of language contacts.