Europe is the cradle of dialectology and in most European countries the study of geographical language variation has an almost century long tradition. In fact, regional variation and the dialects of all the national and most of the indigenous minority languages spoken in Europe have been the topic of scientific research. Classifications of dialects and dialect groups have been produced for each of these languages. Despite the numerous language-centred dialect studies and studies focussing on dialect variation across language borders and on larger geographical areas, such as Europe (e.g., Atlas Linguarum Europae, European Dialect Syntax), there is no publication that attempts to collect and analyse the dialect classifications in the endogenous languages spoken in Europe. DIACLEU, Dialect Classifications of Languages in Europe, proposes to fill this gap, in a series of issues that will be published in this journal.