This book surveys linguistically Celtic geographical names of Eastern Europe which are known from ancient and early medieval written sources and epigraphy. They normally form enclaves of toponyms sometimes accompanied by ethnic name(s), and quite often these areas are associated with the Celts by the authors of antiquity or in archaeological investigations. Before going East, some general and methodological comments on Celtic toponymy are offered, and the geographical names of Celtic or presumably Celtic linguistic origin of Central Europe are discussed. The analysis of enclaves of Celtic geographical names is arranged by modern countries, and the data is observed from linguistic and philological standpoints.