For many centuries, Upper Silesia was the scene of intensive language contact between a continuum of West Slavic dialects (or the Polish and Czech languages) and German colonists, mainly in the 13th century. The process of colonisation under German town law led to the establishment of hundreds of new towns and villages, some with German names. The oldest historical sources for Upper Silesia are Liber fundationis episcopatus Vratislaviensis (Book of endowments of the Bishopric of Wrocław), dating back to c 1305, as well as registers of such endowments from c 1325. German medieval place names in Upper Silesia are a minority, and no such town names can be found in many areas. This article is an analysis of the percentage of German place names in relation to all place names [in Upper Silesia]. It defines the areas with the largest number of such names and contains a linguistic analysis of the names. Interestingly, the area with the largest number of German place names is the Duchy of Teschen, with the castellany of Oświęcim (which was once part of the Duchy of Teschen), the neighbouring part of the Duchy of Racibórz and the western part of the Duchy of Opole. In the Duchy of Bytom (the Siewierz part of which no longer belongs to Upper Silesia), German place names were not very common. For the areas covered by the Diocese of Kraków, the names of parish priests are known as well. The presence of the German name of parish priests in towns and villages with German place names half a century from their establishment indicates that German people may have lived there, especially because it is certain in some cases that they did.